WO2001080581A1

WO2001080581A1 - Method and means in a telecommunication system

Info

Publication number: WO2001080581A1
Application number: PCT/SE2001/000767
Authority: WO
Inventors: Bert Hansson
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2000-04-18
Filing date: 2001-04-06
Publication date: 2001-10-25
Also published as: SE516977C2; SE0001304D0; SE0001304L; AU2001248948A1

Abstract

The present invention relates to a method and means for estimating the traffic load in a cell in a radio communication system. A base station measures (301) a first interference level in the cell. The base station transmits (302) a turn-off message to all radio units in the cell. The radio units in the cell determines (307) if they are in low power saturation, i.e. their output powers have been reduced to their minimum output power level and they still exceed the output power that is needed to comply with the SIR requirements in the system (e.g. by being very close to the base station). All radio units except those determined to be in low power saturation turn off their transmitters (308) while the base station measures (309) a second interference level in the cell. The base station estimates the traffic load (310) from the difference between the first and second interference level.

Description

Method and means in a telecommunication system

TECHNICAL FIELD OF THE INVENTION

The present invention relates in general to the field of telecommunication and, in particular, to a method and means for estimating the traffic load in a cell in a cellular radio communication system.

DESCRIPTION OF RELATED ART

By "radio unit" is meant all portable and non-portable equipment intended for radio communication, like mobile/cellular phones, transceivers, pagers, telex, electronic notebooks, laptops with integrated radios, communicators, computers, routers, tailored microchips or any other electronic equipment using a radio link as a mean of communication. These equipments can be used in any type of radio communication system, such as cellular networks, satellite or small local networks.

Cellular radio communication systems, e.g. D-AMPS, GSM and CDMA (IS-95, CDMA 2000, CDMA etc) , are commonly employed to provide speech and data communications to a plurality of subscribers with radio units.

These systems generally include a number of radio nodes (e.g. base stations) serving radio units, one or more control nodes and at least one switching node or similar. A typical cellular radio communication system may include hundreds of base stations, thousands of radio units and at least one switching node .

A cellular radio communication system covers a certain geographical area. This area is typically divided into specific regions, e.g. cells. A cell typically includes a base station and the radio units with which the base station is in communication. The cell associated with the particular base station with which a radio unit is communicating is commonly called the serving cell.

There are mainly two types of channels in cellular radio communication systems, the physical and the logical channels. A physical channel is a carrier of information on a radio link (a layer 1 channel) . A logical channel (a layer 2 channel) is a specific kind of information transmitted on a physical channel, e.g. speech on a traffic channel. A common expression is that the logical traffic channel is "mapped" on the physical channel. In WCDMA systems there are also a third type of channels, the transport channels. A transport channel is used for communication between a layer 1 and a layer 2 channel, i.e. a logical channel is mapped on a physical channel via a transport channel. Channels that are mentioned in this text and which are not explicitly stated as physical or transport channels are mainly logical channels.

The cellular radio communication systems usually provides a broadcast channel on which all radio units can listen to system information from the base stations, e.g. the Broadcast Control Channel (BCCH) in GSM and CDMA systems. The BCCH is mapped on a Primary Common Control Physical Channel (P-CCPCH) in WCDMA.

The BCCH is one example of a common control signalling within a cellular radio communication system. Another example is paging signalling which is used to wake and/or reach a radio unit as an initial step when somebody in the radio system or in the ordinary exchange system connected to the radio system is trying to reach the radio unit. The paging message is transmitted through the radio system (direct or in steps, local area by local area) to find the radio unit. There are paging channels in both GSM and CDMA systems, e.g. in WCDMA where there is a paging control channel PCCH mapped on a Secondary Common Control Physical Channel (S-CCPCH) . There is a limit in a CDMA system for the number of radio units that can be used simultaneously. This limit is determined by the maximum allowed interference in the system. The more radio units that are used the bigger interference is generated in the system. An admission control function will start to reject radio units that want to access the system if the maximum number of simultaneous users have been reached. This is to guarantee a certain minimum quality on the radio traffic in the system.

The interference in a cellular radio communication system could be divided in interference from the same cell, called intracell interference, and interference from neighboring cells, called intercell interference. The interference measured at the base station in a CDMA system is often used by a traffic load detector to estimate the traffic load in the cell as the interference grow with the traffic load. Generally the base station has a power detector that measures the total received power, i.e. the interference level. This means that the detector measures both the intracell and intercell interference. The measured interference is approximated to be proportional to the traffic load in the cell at high traffic. This is a reasonable approximation if the intercell interference can be neglected compared with the intracell interference. However, this is often a to optimistic approximation in a CDMA system. Especially when there are radio units in low power saturation near the base station. These radio units are using the lowest possible output power and still exceeds the output power that is needed to comply with the Signal to Interference Ratio (SIR) requirements in the system. This is due to the fast power control limitation in the CDMA systems. Radio units in low power saturation generate higher intracell interferences than the other radio units in the cell. Radio units who are so close to the base station that their minimum output power exceeds the necessary output power are called radio units in low power saturation. The interference from one radio unit in low power saturation might be equal to the interference from a number of radio units that are not in low power saturation and the traffic load detector will give a bad estimation of the actual traffic load (a poor accuracy) . Such a bad traffic load estimation can result in that the system starts to reject radio units that wants to access the system because the system thinks that the maximum number of simultaneous users have been reached. This means that the system will loose capacity. Hence, there is a need for a method and means that uses interference measurements for estimating the traffic load in a cell with a higher accuracy than those used today.

The PCT application WO 95/26598 describes a CDMA system arranged to solve a problem regarding low call quality due to too many simultaneous users in the system. This is solved by using a central control unit that calculates average mutual interference's which are used in an optimisation process for acquiring an access control in different radio zones of the system. This means that the number of simultaneous users in each radio zone can be limited to a certain maximum number to maintain a good call quality in each radio zone. Interference measurements are performed in each radio zone to be able to calculate the average mutual interference in the system. In one embodiment the radio base station and all mobiles in one specific radio zone are temporarily inhibited to transmit for a short period to measure the interference from the neighbouring radio zones. This measurement together with similar measurements from other radio zones are then forwarded to the central control unit which resolves the average mutual interference's in the system.

The US patent US 5 774 814 describes a method and system for detecting and receiving radio signals employing a modified macrodiversity (base station diversity) scheme. Multiple versions of a signal are detected by receivers and base stations and are employed by a decision algorithm to determine the information. At least three different signals are processed/combined to get the desired information. To determine some of the parameters for the algorithm the signal to interference ratio for each mobile is estimated by ordering one mobile at the time in a cell to turn off its transmitter shortly so that the interference from the other mobiles can be measured. When the mobile is switch on the total interference level is measured, whereby the interference for that particular mobile that has been switched off can be calculated. Some coordination is performed to avoid that more than one mobile at the time is switched off.

As will be seen herein, the systems and methods disclosed in WO 95/26598 and US 5 774 814 are of different types than the method and means of the present invention.

SUMMARY

The present invention meets a problem related to traffic load estimation in a cell based on interference measurements in a cellular radio communication system and especially in a CDMA system, e.g. WCDMA.

The problem is that the traffic load estimation, which is based on an interference measurement in the cell, is disturbed by interferences from radio units in low power saturation, i.e. radio units that are close to the base station, as well as interferences from radio units in neighbouring cells and/or other types of equipments that generates interferences. This means that the traffic load estimation may get a very poor accuracy in some situations.

In light of the foregoing, a primary object of the present invention is to provide a method and means for improving the accuracy for traffic load estimations using interference measurements to estimate the traffic load.

Another object of the present invention is to provide a method and means to avoid that interferences from radio units in low power saturation interfere with the traffic load estimation.

In a method according to the present invention, a first interference level is measured in the cell. Transmitters in selected radio units in the cell are switched off while a second interference level is measured. The traffic load is then estimated from the first and second interference value.

According to one embodiment of the method, the base station in the cell measures a first interference level. Radio units in the cell that are not in low power saturation then temporarily switch off their transmitters while a second interference level is measured by the base station. The traffic load is then estimated as the difference between the first and second interference value .

The inventive method is therewith characterised as it appears from the appended claim 1.

A system according to the present invention comprises means for measuring a first and a second interference level, means to temporarily switch off the transmitters in specific radio units and means for estimating the traffic load from said first and a second interference level .

An advantage with the present invention is that it is possible to exclude the interference from neighbouring cells when estimating the traffic load.

Another advantage is that it is possible to exclude the interference from radio units in low power saturation when estimating the traffic load. Still another advantage is that it is possible to exclude the interference from other equipments than radio units when estimating the traffic load.

Yet another advantage is that the same measurement unit can be used for all interference measurements, whereby any measurements faults are automatically suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is illustrating a schematic view of a part of a cellular radio communication system.

Figure 2 is illustrating a schematic view of a cell in a cellular radio communication system.

Figure 3 is illustrating a flow chart of a first embodiment of a method according to the present invention.

Figure 4 is illustrating a flow chart of a fourth embodiment of a method according to the present invention.

Figure 5 is illustrating a flow chart of a fifth embodiment of a method according to the present invention.

Figure 6 is illustrating a flow chart of a sixth embodiment of a method according to the present invention.

Figure 7 is illustrating a schematic block diagram of a system for utilising the method according to the present invention. DETAILED DESCRIPTION OF EMBODIMENTS

The present invention relates to a method and means for estimating the traffic load in a cellular radio communication system and especially in a CDMA system, e.g. WCDMA.

Figure 1 illustrates a schematic view of a part of a cellular radio communication system including a number of cells 101-104, base stations 105-108 and radio units 109-114. The base stations 105-108 can be connected to one or more mobile switching centres, radio network controllers (RNC's), routers or similar nodes (not illustrated in figure 1).

Figure 2 illustrates a schematic view of a cell 201 in a WCDMA system. A base station 202 serves a number of radio units 203- 208 in the cell. The dashed circle 209 around the base station 202 illustrates the distance from the base station in which the minimum output power from the radio units can be used to reach the base station with a sufficient signal to interference ratio (SIR), i.e. SIRτarget- Both an inner control loop (a fast power control) and an outer control loop controls the output power. The radio unit output power can be adjusted within a specified dynamic range, e.g. 70dB, by the control loops (i.e. between a maximum and a minimum output level) . This means that there is a lower limit for the output power, i.e. the minimum output level . A common value for the minimum output power in a WCDMA system is -44dBm.

The dynamic range of the radio unit is a compromise between the resolution and the dynamic range in the power control. A high dynamic range with high resolution requires several bits to control the power levels and this increase the radio units power consumption when the bits are processed. One reason for limiting the dynamic range of the radio unit is to reduce the power consumption. Another reason is to make the test of the radio units in the production fast and simple since a large dynamic range takes a longer time to be tested. The radio units 207 and 208 inside circle 209 are radio units in low power saturation. Their output powers where reduced to the minimum output power by the inner control loop when they passed the dashed circle 209 on their way towards the base station 202. This means that these radio units are so close to the base station that their minimum output powers exceed the output power needed to keep the SIRτarget- This also means that they cause a lot of interference in the base station 202. The fast power control can only increase the current output power and that will not happen as long as they are within the circle 209. Hence, radio unit 207 and 208 are said to be in low power saturation. As mentioned before the interference from a few radio units in low power saturation might cause an admission control function in the system to reject new radio units that wants to access the system well before the allowed maximum number of simultaneous users in the system is reached. Due to the interference from a few radio units in low power saturation the traffic load is estimated to be bigger than it actually is.

The radio units 203-206, which are further away from the base station than radio units 207 and 208, can still both increase and decrease their output powers (depending on their movement within the cell) which means that they are not in low power saturation .

As mentioned above, the system has at least two different ways of controlling the output power from the radio units and the base stations, i.e. the inner and the outer control loop.

The inner control loop (the fast power control) on the uplink means that the base station measures the SIR from the radio units and compare those measured SIR values with reference SIR values (SIR_Targ_ets) • These SIR_Targ_et are minimum SIR values chosen to optimise the system performance, e.g. regarding capacity. If a measured SIR is higher than the SIR_Target for a specific radio unit, that radio unit is instructed to reduce the output power by a pre-determined value. If the measured SIR is lower than the SIR_Target that radio unit is instructed to increase the output power by a pre-determined value. This is performed regularly, e.g. several times in each frame. The fast power control enables the base station to balance the received power in the base station to a level guaranteeing all uplink (radio unit to base station communication) channels the required signal to interference ratio (SIR_Target) • The downlink works in a similar way.

The outer power control loop means that a control node measures the quality, e.g. Bit Error Rate (BER) , Frame Error Rate (FER) or Block Error Rate (BLER) , on one or more uplink radio connections and compares it with a reference value (a quality target) . If the quality on a radio connection is higher than the quality target the control node instructs the base station to reduce the SIRτ_arget (e.g. in soft handover in CDMA) to a lower value so that the quality target is reached. If the measured quality is lower than the quality target the control node instructs the base station to increase the SIR_Target. This is performed continuously with a time interval that is longer than the one used for the inner control loop. The outer control loop is usually controlled by a Radio Network Controller (RNC) or similar in the core network.

There is usually a third way of controlling the output power from the radio units and the base stations, and that is the open power control loop. The open power control loop has a slower updating of the radio unit output power than the inner and outer power control loops (closed loop power controls) . Radio units controlled by the open loop and radio units controlled by the closed loops behaves in a similar way.

The radio units are using different kinds of services S, e.g. voice, data and real time services such as video. These services have different SIR_Target depending on the quality target and service bit rate for each type of service S. The total interference experienced by a base station could be divided into intracell interference, intercell interference, interference from radio units in low power saturation, thermal noise from the antenna connector and other interference's.

The intracell interference is a result of the transmission from/to radio units in the cell.

A first part of the intracell interference in the cell is the interference caused by radio units which are not in low power saturation. These radio units may be using one or several services S. If a first number of radio units Ni are using a first type of service S₁ with an SIR_Target SIR-ri and a second number of radio units N₂ are using a second service S₂ with an SIRτ_arg_et SIR_τ2, the first part of the intracell interference Ii in the cell can be expressed as:

Ii = I* (Ni* SIR_TI + N₂* SIR_T2) (equation 1)

This means that if the number of radio units in the cell is Z the received intracell interference Ii can be described as: z Ix≡^tl - ∑SIRr_j, (equation 2)

«=ι where SIR_T,_n = SIR_Target (C/I) for radio link number n, from radio unit number n.

A second part of the intracell interference in the cell is the interference caused by radio units in low power saturation. As stated before, these radio units may cause big intracell interference because they are close to the base station and have a higher SIR than the SIR_Targef The received interference at the base station from radio units in low power saturation is expressed as I_PL.

Intercell interference is the interference a specific cell experiences from other (mostly neighbouring) cells. The intercell interference is depending on radio net planning parameters like, cell to cell distance (parameter a) , number of neighbouring cells (parameter b) , radio net environment (parameter c) , traffic load in surrounding cells (parameter d) , etc. This means that the intercell interference could be described as a function I(a,b,c,d, ....).

The thermal noise at the antenna connector is also a source for interference. This is expressed as Inoi_se-

The last part of the total interference is the interference generated by other systems and/or equipment's, e.g. household equipments. This interference is expressed as I_di_s -

The total received interference I in the base station receiver can then be expressed as: z I =I - SIR_T_„ + I(a,b,c,d, .... ) + I_PL + I_dist + I_nθi_Se (equation 3)

Where SIR=C/I.

This illustrates that the interference I measured by a base station is equal to the traffic load in the cell plus a number of additional interference factors such as I(a,b,c,d, ....), I_PL,

Idist and Inoise •

According to the present invention the traffic load in cell 201 is approximated to be equal to the interference caused by the fast power controlled radio units 203-206, i.e. all used radio units in cell 201 except those that are in low power saturation

(207 and 208) . Although the radio units in low power saturation are contributing to the radio traffic in the cell their exclusion does not affect the accuracy of the traffic load estimation in any major way. This is because they are so few compared to the number of other radio units (radio units not in low power saturation) in the cell. In fact the exclusion of radio units in low power saturation enhances the accuracy of the traffic load estimation compared to known methods because they generate much more interference than the corresponding number of radio units that are not in low power saturation. The part of the interference in the cell, which originates from the radio units in low power saturation, is not proportional to their part of the traffic load as it is with the other radio units in the cell.

Figure 3 illustrates a flow chart of a first embodiment of a method according to the present invention. References in the text below will also be made to figure 2.

According to a step 301 in figure 3, the base station 202 in cell 201 measures a first interference level I (see equation 3) in cell 201.

According to a step 302, the base station transmits a paging signal to all radio units 203-208 in the cell on a first channel, e.g. a paging control channel (PCCH) . The paging signal includes information regarding a second radio channel, e.g. a forward access channel (FACH) (which is a common transport channel in WCDMA) , that the radio units shall listen to for further information. The paging signal in this step is a first example of common signalling. According to a step 303, the radio units 203-208 start to listen on the second radio channel.

According to a step 304, the base station 202 transmits a turn- off message to the radio units on the second channel. The message includes information regarding in which time slot the radio units shall turn off their transmitters (a transmission in a WCDMA system is divided into frames that includes 15 time slots) . This time slot corresponds to a determined time period that is sufficient for the measurement in step 309 to be performed. The duration of this determined time period is dependent on the performance and construction of the radio communication system. This means that the determined time period might be increased to last for two or more time slots or decreased to last during only a part of a time slot in some radio communication systems (i.e. the turn-off message will include information regarding a part of a time slot or two or more time slots in which the radio units shall turn off their transmitters) . According to a step 305, the radio units receive the turn-off message from the base station and set their timers in accordance to the turn-off message. These timers (or counters) are arranged in the radio units and are used to keep track of the turn off time (or time slots) after they receive the turn off message.

According to a step 306, the timers in the radio units start to count down .

According to a step 307, each radio unit 203-208 determines if it is in low power saturation when the turn off time is about to be reached. Those radio units that are in low power saturation, e.g. radio unit 207 and 208, disregard the turn-off message (i.e. they skip the next step 308) .

According to the step 308, the radio units not in low power saturation turn off their transmitters during the time slot (or slots) that was indicated in the turn-off message received in accordance with step 30 . These radio units are a selected number of radio units in the cell.

According to a step 309, the base station 202 measures a second received interference level I_Co_rr (I_corr=I (a,b, c, d, ...) +I_PL+I is+Inoise) during the transmitter turn-off in step 308. The second received interference level includes the second part of the intracell interference I_PL because radio units in low power saturation, e.g. 207 and 208, are not turned off during this measurement.

According to a step 310, the traffic load in cell 201 is estimated in the base station by calculating the difference between the first interference level I, measured in step 301, and the second interference level I_CORR measured in step 309

(i.e. the traffic load = I - I_COrr) • The traffic load estimation may as an alternative be made in a control node (e.g. in a Radio Network Controller, RNC) , which means that the base station forwards the measurement results in step 301 and 309 to the control node. Any measurement errors are suppressed as both the first and the second interference levels are measured by the same base station (and the same detector/measurement unit in the base station) and as the estimated traffic load is calculated from the difference between theses two levels.

The order in which these steps are performed can be changed, e.g. the measurement of the second interference level in step 309 can be performed before the measurement of the first interference level in step 301, which means that steps 302-309 are performed before step 301.

In a second (not illustrated) embodiment of a method according to the present invention a second example of common signalling is used. A broadcast channel, e.g. a Broadcast Control Channel (BCCH) , is used instead of the paging signal whereby steps 302- 303 according to figure 3 are omitted and the base station transmits the turn-off message to the radio units on the BCCH channel in step 304. The other steps in the second embodiment are similar to the corresponding steps in the first embodiment according to figure 3.

In a third (not illustrated) embodiment of a method according to the present invention the common signalling is replaced by dedicated signalling. Steps 302-303 according to figure 3 are omitted and the base station transmits the turn-off message to all radio units in the cell on a dedicated channel in step 304. The other steps in the third embodiment are similar to the corresponding steps in the first embodiment according to figure 3. An example of a dedicated channel is the Dedicated Control Channel (DCCH) .

One example of where dedicated signalling can be used in WCDMA is together with compressed mode. Compressed mode can be used to create the determined turn-off periods for the measurement in step 309. Compressed mode is specified by 3GPP (TS.25.215) and is intended for use in hard handover situations, i.e. handover to a carrier with another frequency (in another system or within the same system) .

It is also possible in the present invention to use a specific channel for transmissions of the turn off messages between base stations and radio units.

Figure 4 illustrates a flow chart of a fourth embodiment of a method according to the present invention, where all radio units except those in low power saturation receives the turn- off message transmitted from the base station.

According to a step 401 in figure 4, the base station 202 in cell 201 measures a first interference level I (see equation 3) in cell 201. According to a step 402, the base station determines which radio units are in low power saturation by checking in a memory in which information regarding radio units that are detected to be in low power saturation are stored. The base station continuously detects all neglected orders to lower the output power that are sent to the radio units. If as an example 10 consecutive orders to reduce the output power have been neglected by a radio unit it is determined to be in low power saturation .

According to a step 403, the base station transmits the turn- off message on dedicated control channels to the radio units that shall turned off their transmitters, i.e. all radio units except those in low power saturation. Steps 404-405 are equal to steps 305-306 and steps 406-408 are equal to steps 308-310 in the first embodiment according to figure 3 and will for simplicity not be described again.

Figure 5 illustrates a flow chart of a fifth embodiment of a method according to the present invention in which radio units that are using a specified service S but are not in low power saturation are turned off during the second interference measurement. This means that it is possible to estimate the traffic load for one or more specified services in the cell.

According to a step 501 in figure 5, the base station 202 in cell 201 measures a first interference level I (see equation 3, page 12) in cell 201.

According to a step 502, the base station transmits the turn- off message to the radio units on a dedicated channel, e.g. a DCCH . The turn off message includes information regarding in which time slot (or slots) the radio units shall turn off their transmitters and information regarding which service or services that are to be turned off, e.g. all voice services. The turn off message may also be transmitted by common signaling according to the first and second embodiment.

According to a step 503, the radio units receive the turn-off messages from the base station and set their timers in accordance to the turn-off message.

According to a step 504, the timers in the radio units start to count down.

According to a step 505, each radio unit 203-208 determines if it is in low power saturation. Those radio units that are in low power saturation, e.g. radio unit 207 and 208, disregard the turn-off message (i.e. they skip the next two steps 506- 507) . According to a step 506, each radio unit determines what kind of service it is using. Those radio units that are not using the service or services according to the turn-off message received in step 502 disregard the turn-off message (i.e. they skip the next step 507) .

According to the step 507, the radio units that are using the service or services according to the turn-off message received in step 502 and are not in low power saturation turn off their transmitters during the time slot (or slots) that was indicated in the turn-off message received in accordance with step 503. These radio units that are a selected number of radio units in the cell .

The last steps 508-509 in figure 5 are equal to steps 309-310 according to figure 3 and will for simplicity not be described again.

Figure 6 illustrates a flow chart of a sixth embodiment of a method according to the present invention where a compensation of the propagation delay between the radio units and the base station is performed. References in the text below will also be made to figure 2.

The first steps 601-603 in figure 6 are equal to steps 301-303 according to figure 3 and will for simplicity not be described again.

According to a step 604, the base station 202 determines an uplink correction factor Δti for each radio unit in the cell

(The uplink time correction factors Δt may also be determined in a control node, e.g. a Radio Network Controller, connected to the base station) .

According to a step 605, the base station 202 transmits the turn-off message to the radio units. This transmission can be done by using one of the two common signalling examples according to the first and second embodiment or by dedicated signalling according to the third embodiment. The message includes information regarding in which time slot (or slots) on the uplink the radio units shall turn off their transmitters and the correction factors Δti determined in step 604.

According to a step 606, the radio units receive the turn-off message from the base station 202, set their timers in accordance with the turn-off message and the correction factors

Steps 607-611 are equal to steps 306-310 in the first embodiment according to figure 3 and will for simplicity not be described here again.

The (uplink) correction factors Δti are time compensation factors which are used to compensate for the different propagation delays between the radio units and the base station. This facilitates a more synchronised turn-off for all radio units in the cell. Each radio unit will receive a specific correction factor that is determined in step 604 in the sixth embodiment. The radio units turn off their respective transmitter Δti in advance of the given time slot(s) and the base station will experience as if they are turned off at the same time.

There are several ways to use a Δti correction factor. One way is to just turn-off the transmitter at the time instant compensated by the Δti correction factor. Another way is to turn-off the transmitter compensated with the Δt correction factor, and make an additional frame time advance of the mobile uplink in phase to guarantee a symbol synchronous received turn off at the base station receiver.

One example of determining the correction factors is to determine the distance Δd between the radio unit and the base station. The correction factors are then calculated as Δti= (2*Δdi) /v, where v is the speed of the radio signal and Δdi the distance between the base station and radio unit number i.

One example of determining the distance Δd between a radio unit and a base station is to use a positioning system to determine the position of the radio unit. The position of the base station is known whereby the distance Δd is determined from these two positions. There are a number of well-known positioning systems that can be used e.g. the Global Positioning System (GPS) .

Anther example of determining the distance Δd is to use the receiver delay spread in the base station receiver.

Due to multipath propagation, the transmitted signal from a radio unit will be received as a number of mutually delayed replicas in the base station receiver. All replicas of the signal are received and merged together to one reception signal in the base station receiver. Since the radio unit is synchronized to the base station in the downlink, the position of the received cluster of multipaths signals gives the relative position of the radio unit. A radio unit that is moving towards the cell edge has a multipath cluster that is moving relatively in time. The first received path can be considered to take the shortest way from the radio unit to the base station. The relative time position of this path compared to the delay of the first receiver path for a radio unit at the center of the cell gives the shortest possible distance d_x between the radio unit and the base station. This means that the distance Δd can be estimated to be equal to the distance d_x.

If the radio unit transmitter to receiver timing is allowed to change, e.g. as specified by 3GPP in TS 25.214 for WCDMA, the radio unit or the control node (e.g. the RNC) could adjust the correction factor Δti with the timing difference.

Other examples of determining the Δti is to use a round trip delay measurement or a Round Trip Time measurement (RTT) (defined in the 3GPP specification TS 25.215).

The base station or the control node can as an alternative determine (select) the specific time slot(s) or part of a time slot (in which the transmitters in the radio units shall turn- off) in such a way that this time compensation is "automatically" made when the transmitters are turned-off during the given time slot(s), i.e. the time compensation is made in the radio or control node by time advance shift of the downlink. This means that no correction factors Δt needs to be transmitted to the radio units.

Note that the radio units in neighbouring cells should preferably not be turned off at the same time as the radio units in the cell where the second interference measurement, e.g. in step 309, is to be measured in order to get the best possible estimation of the traffic load. A control unit in the system can as an example provide a scheduling or control function that prevents that neighbouring base stations transmit their turn-off messages at the same time.

In the above mentioned embodiments the radio units in low power saturation are not considers as traffic load to avoid the error caused by their disproportionately big interference and thereby enhance accuracy of the traffic load estimation.

In a seventh (not illustrated) embodiment of a method according to the present invention a radio unit traffic load compensation factor ΔRU is used to include even the small traffic load originating from those few low power saturated radio units that are excluded in the above mentioned embodiments. The SIRt_arget for these low power saturated radio units are known by the base station. Each radio unit that determines/detects that they are in low power saturation (e.g. according to step 307) transmits a low power saturation detect signal to the base station which thereby always know how many radio units in the cell that are in low power saturation (n_LPS) . The base station may as an alternative determine the number of radio units in low power saturation n_LPS according to step 402 in the fourth embodiment. The radio unit traffic load compensation factor ΔRU is then estimated in the base station as: n_LPS*I*SIR_Target • The base station (or RNC) estimates the traffic load according to step 310, and adds the radio unit traffic load compensation factor ΔRU to the calculation of the traffic load, i.e. the traffic load is estimated as: I+ΔRU-I_COrr-

The turn-off message in the present invention may as an alternative include a specific turn-off parameter instead of the given time slot(s). The turn-off parameter is then used by the respective radio unit to select a turn-off profile from a table or a list that is stored in the radio unit. The turn-off profile indicates in/during which time slot(s) the uplink channels from the transmitters in said selected number of radio units should be turned off.

If a lower accuracy in the estimation of the traffic load is accepted step 307 and 308 according to the first embodiment (and the corresponding steps in the other embodiments) may be omitted, whereby the interference from the radio units in low power saturation are excluded in the second interference measurement in step 309.

Figure 7 illustrates a schematic block diagram of a part of a cellular radio communication system for utilising the method according to the present invention. The system 700 includes a radio unit 701, a base station 702 and a control node 703 (e.g. a Base Station Controller, a Radio Network Controller or a router for internet access) connected to the base station 702. The control node 703 can as an example be connected to a switching node, a gateway, or an external communication system (not illustrated) . The radio unit 701 and the base station 702 comprises known circuits and functions for known operations plus some additional units for carrying out the present invention. These units may perform each method step by way of hardware components, a computer or processor programmed by appropriate software or by any combination of hardware and software.

The radio unit 701 includes at least a timer unit 704, a low power saturation check unit 705, a transmitter turn off unit 706, a transmitter 708, a power control unit 709, a receiver 710 and (if the fifth embodiment of the method is to be used) a check service unit 707.

The timer unit 704 stores the turn off time and starts to count down, e.g. according to steps 305-306. In the sixth embodiment this unit also adds the time compensation factor (in step 606) received from the base station before the count down starts. The low power saturation check unit 705, which is connected to the power control unit 709, determines if the radio unit is in low power saturation according to step 307. The low power saturation check unit 705 includes a detector that detects the current output power level. The low power saturation check unit 705 compares the detected current output power level with the minimum output level. The transmitter turn off unit 706, which is connected to the power control unit 709, the timer unit 704, the transmitter 708 and/or the receiver 710, is arranged to turn off the transmitter 708 as in step 308 when the timer unit 704 has reached the time for turn off, i.e. the right time slot (s) .

The check service unit 707, which is connected to the transmitter turn off unit 706, the transmitter 708 and/or the receiver 710, is used in the fifth embodiment of the method where the service or services the radio unit is using is determined, e.g. by checking the channels that are used in the uplink .

The base station 702 includes at least a turn off decision unit 711, an interference measurement unit 712, a traffic load estimating unit 713, a receiver 715 and (if the fourth embodiment is to be used) a low power saturation check unit 714.-

The turn off decision unit 711 decides when the turn off message is to be transmitted, i.e. when the base station wants to measure the interference, e.g. according to step 309. The interference measurement unit 712, which is connected with the receiver 715, performs the interference measurements according to step 301 and 309. The traffic load estimating unit 713 performs the estimation, e.g. in according to step 310, and includes a calculator unit (not illustrated) for calculating the I-I_cor_r or the I+ΔRU-I_corr. If the fourth embodiment is to be utilised, the base station 702 also includes a low power saturation check unit 714, which determines if radio units are in low power saturation by continuously detecting all neglected orders to lower the output power that are sent to the radio units. If as an example 10 consecutive orders to reduce the output power have been neglected by a radio unit (i.e. the SIR from the radio unit is still higher than the SIR_Targe_t) it is determined to be in low power saturation.

The decision to turn off the radio units in each cell can as an alternative be made in the control node 703 instead of the base station 702. This means that the turn off decision unit 711 is arranged in the control node 703 (not illustrated) . The traffic load estimating unit 713 can also, as an alternative, be arranged in the control node 703 (not illustrated) . This means that the calculation of the I-I_Corr or the I+ΔRU-I_corr is performed in the control node. The decision to turn off the radio units in each cell might also be an integral part of the regular system behaviour, i.e. configured in the system, in such a way that there are certain pre-determined time slots per cell that are always used for the interference measurements according to the present invention.

The inventive methods can completely or partially be implemented as software in a cellular radio communication system, e.g. in radio units, base stations, radio network controllers etc.

Claims

1. A method for estimating the traffic load in a specific region (101-104, 201) of a radio communication system, where at least one radio node (105-108, 202) is arranged for communication with radio units (109-114, 203-208) in said specific region, said method comprises the following steps:

measuring a first interference level (301,401,501,601) in said specific region at said at least one radio node;

c h a r a c t e r i s e d in that said method further comprises the following steps: turning off (302-308,402-406,502-507,602-609) the transmitters in a selected number of said radio units in said region during a determined time period; measuring a second interference level (309,407,508,610) in said specific region at said at least one radio node during said determined time period; and estimating said traffic load (310,408,509,611) from said first and second interference level.

2. The method as claimed in claim 1, wherein said step of turning off the transmitters in a selected number of radio units comprises the following steps: transmitting a turn-off message (302-304,602-605) from said at least one radio node to said radio units in said specific region; determining in said radio units (307,608) if they are in low power saturation; and turning off the transmitters (308,609) in all radio units in said specific region except in those radio units that are determined to be in low power saturation.

3. The method as claimed in claim 1, wherein said step of turning off the transmitters in a selected number of radio units comprises the following steps: transmitting a turn-off message (502) from said at least one radio node to said radio units in said specific region, wherein said turn off messages includes information regarding at least one specific service that should be turned off; determining in said radio units (505) if they are in low power saturation; determining in said radio units (506) what kind of service said radio units are using; and turning off the transmitters (507) in all radio units that are using said at least one specific service in said specific region except in those radio units that are determined to be in low power saturation.

4. The method as claimed in claim 2 or 3, wherein said step of transmitting a turn-off message from said at least one radio node to said radio units in said specific region comprises the following step: transmitting a common message (302,602) from said at least one radio node to said radio units on a common channel, wherein said common message includes said turn off message.

5. The method as claimed in claim 4, wherein said common message is a broadcast message and where said common channel is a broadcast channel.

6. The method as claimed in claim 2 or 3, wherein said step of transmitting a turn-off message from said at least one radio node to said radio units in said specific region comprises the following steps: transmitting a paging signal (302,602) from said at least one radio node to said radio units on a first channel, wherein said paging signal includes information instructing said radio units to temporarily switch to a second channel; and transmitting said turn off message (304,605) on said second channel to said radio units.

7. The method as claimed in claim 2 or 3, wherein said step of transmitting a turn-off message from said at least one radio node to said radio units in said specific region comprises the following step: transmitting said turn-off message (502) from said at least one radio node to said radio units on dedicated channels.

8. The method as claimed in claim 1, wherein said step of turning off the transmitters in a selected number of radio units comprises the following steps: determining in said at least one radio node (402) if any radio units in said specific region are in low power saturation; transmitting a turn-off message (403) on dedicated channels from said at least one radio node to said radio units in said specific region except to those radio units that are determined to be in low power saturation; and turning off the transmitter (406) in those of said radio units in said specific region that received said turn-off message.

9. The method as claimed in any one of claims 2-8, wherein said turn-off message includes information about said determined time period in which the uplink channels from the transmitters in said selected number of radio units should be turned off.

10. The method as claimed in claim 9, wherein said determined time period is specified as at least one timeslot.

11. The method as claimed in claim 9, wherein said determined time period is specified as a specific part of a timeslot.

12. The method as claimed in any one of claims 9-11, wherein said turn-off message includes a correction factor for each radio unit enabling said selected number of radio units to synchronise said transmitter turn off in respect of said at least one radio node, wherein said correction factors are used to compensate for the propagation delays between said radio units and said at least one radio node.

13. The method as claimed in claim 12, wherein said correction factor is calculated as two times the distance between the at least one radio node and the respective radio unit divided by the speed of the radio signal and where said distance is determined from position co-ordinates generated by a positioning system.

14. The method as claimed in claim 12, wherein said correction factor is calculated as two times the distance between the at least one radio node and the respective radio unit divided by the speed of the radio signal and where said distance is determined from the receiver delay spread in said at least one radio node.

15. The method as claimed in any one of claims 2-8, wherein said turn-off message includes a specific turn off parameter and where said turn off parameter is used by said radio units to select a stored turn-off profile in said radio units, and where said turn-off profile indicates when the uplink channels from the transmitters in said selected number of radio units should be turned off.

16. The method as claimed in any one of claims 2-15, wherein said step of estimating said traffic load (310,408,509,611) includes the following steps: determining in said at least one radio node the number of radio units in low power saturation; calculating a traffic load compensation factor in said at least one radio node by multiplying the number of radio units determined to be in low power saturation with said first interference level and with the SIR_Target used by said radio units in said specific region; and estimating said traffic load from said first interference level, said second interference level and said traffic load compensation factor by calculating the difference between said first and second interference level and then adding said traffic load compensation factor.

17. The method as claimed in any one of claims 1-16, wherein said estimation of said traffic load (310,408,509,611) is made in said at least one radio node (105-108,202).

18. The method as claimed in any one of claims 1-16, wherein said estimation of said traffic load (310,408,509,611) is made in a control node (703) connected to said radio node.

19. The method as claimed in any one of claims 1-18, wherein said measuring of a first interference level (301,401,501,601) and said measuring of a second interference level (309,407,508,610) are performed by the same interference measurement unit (712) arranged in said radio node (703) .

20. The method as claimed in claim 1, wherein said selected number of radio units are all active radio units in said region, whereby the transmitters of all of said active radio units are turned off by a turn-off message transmitted from said at least one radio node to said selected number of radio units.

21. A radio communication system having means for estimating the traffic load in a specific region (101-104, 201) of said system, where at least one radio node (105-108, 202) is arranged for communication with radio units (109-114, 203-208) in said specific region, said system comprises:

means for measuring a first interference level (712) in said specific region at said at least one radio node;

c h a r a c t e r i s e d in that said system further comprises: means for turning off (704,706,711) the transmitters in a selected number of said radio units in said region during a determined time period; means for measuring a second interference level (712) in said specific region at said at least one radio node during said determined time period; and means for estimating said traffic load (713) from said first and second interference level .

22. The system as claimed in claim 21, wherein said system comprises means for determining (705,714) if said radio units are in low power saturation.

23. The system as claimed in claim 22, wherein said means for determining (705) if said radio units are in low power saturation are arranged in said radio units.

24. The system as claimed in claim 22, wherein said means for determining (714) if said radio units are in low power saturation are arranged in said radio node.

25. The system as claimed in any one of claims 21-24, wherein said radio units in said system includes means for timing (704) the transmitter turn off.

26. The system as claimed in any one of claims 21-25, wherein said radio units in said system includes means for checking the service they are using (707) .

27. The system as claimed in any one of claims 21-26, wherein said at least one radio node in said system includes means for determining the number of radio units in low power saturation.

28. The system as claimed in any one of claims 21-27, wherein said means for measuring a first interference level (712) and said means for measuring a second interference level (712) are the same means and that said means for estimating said traffic load (713) includes calculation means for calculating a difference between said first and second interference level.