GB2394864A

GB2394864A - Cellular radio telecommunication system

Info

Publication number: GB2394864A
Application number: GB0323325A
Authority: GB
Inventors: Nicholas Dougall Johnson; Neil Philip Piercy; Christopher Moore
Original assignee: IP Access Ltd
Current assignee: IP Access Ltd
Priority date: 2002-10-04
Filing date: 2003-10-06
Publication date: 2004-05-05
Also published as: GB0323325D0; AU2003274303A1; GB0222999D0; WO2004032548A1

Abstract

There is described a cellular radio telecommunication system for reducing interference (both intra-cell and inter-cell) within indoor (40), and between indoor and outdoor cellular radio telecommunication coverage areas, the system comprises a plurality of head units (20) throughout the indoor coverage area (40) each being connected to a master unit (10) such that, in combination, they are seen by User Equipment (UE) (50) as a single base station using a single carrier. The master unit (10) continuously ranks the head units (20) by comparing their uplink quality indicators (e.g. by received power or by signal quality) and selectively routes signalling and data traffic via the highest ranked head unit(s) (20). Accordingly, the transmit power of each head unit (20) and UE (50) can be independently controlled and minimised. Interference is therefore reduced by (i) ensuring minimal transmit powers; and (ii) reducing the number of cell boundaries within the indoor coverage area.

Description

À 1 Cellular Radio Telecommunication System 3 This invention relates to a

cellular radio 4 telecommunication system, and in particular, but not 5 exclusively, to a system for reducing interference 6 within indoor, and between indoor and outdoor, 7 cellular radio telecommunication coverage areas.

9 Cell planning in a cellular network is problematic 10 in situations where indoor users are covered by both 11 outdoor and indoor base stations. The existence of 12 walls, ceilings and other obstructions which cause 13 attenuation is compensated for by increasing the 14 transmit power of the Base Stations (BS) and the 15 User Equipment (UK) that is communicating with the 16 BS. In the outdoor environment, the increased BS 17 transmit power increases the interference between 18 neighbouring cells (outdoor inter-cell 19 interference). It also increases the interference 20 power as measured by every other UE within the same 21 cell (outdoor intra-cell interference). In the 22 indoor environment, the increased UE transmit power

:: fe.::: le À c:..::.

1 increases the interference as measured by an indoor 2 BS that may be operating on a similar frequency.

4 A more efficient solution is to provide cover for 5 indoor UE's from indoor BS's and provide cover for 6 outdoor UE's from outdoor BS's. In this case the 7 outdoor cells do not have to increase their transmit 8 power to reach indoor UE's with a corresponding 9 reduction of outdoor intra-cell and outdoor inter 10 cell interference.

12 However, as a consequence, the interference between 13 outdoor BS and indoor BS (the outdoor to indoor 14 inter cell interference) will increase as the indoor 15 traffic amount increases. The worst case scenario 16 is that service levels and coverage as provided by 17 an outdoor BS is reduced in a zone located close to, 18 but just outside of, the indoor environment.

20 The size of the zone, in which indoor to outdoor 21 inter cell interference is service affecting, can be 22 controlled by indoor cell location and indoor cell 23 transmit power. Indoor cell transmit power is a 24 factor of the indoor cell radius. Therefore, a 25 larger number of smaller radius indoor cells can be 26 used to provide indoor coverage with reduced 27 transmit power and thus reduced indoor to outdoor 28 inter cell interference.

30 The outdoor cellular network is disturbed least if a 31 large number of small radius cells are deployed in 32 the indoor environment. Unfortunately, in this

: I: #: À ce : ece::: ee e:e:: .: 1 scenario, the indoor environment suffers from an 2 increase in the indoor inter cell interfence due to 3 the large number of cell boundaries.

5 For a Code Division Multiple Access (CDMA) based 6 system, intra-cell and inter-cell interference 7 reduces cell capacity and range and increases the 8 probability of call drop-out. Reduction of inter 9 cell interference and intra-cell interference is 10 critically important in CDMA cellular systems due to 11 the small number of carriers available for frequency 12 planning.

14 According to a first aspect of the present 15 invention there is provided a cellular radio 16 telecommunication system for reducing cell phone 17 signal interference in a cellular radio 18 telecommunication network, said system comprising a 19 plurality of head units (20) spatially separated 20 throughout a first coverage area (40), wherein each 21 head unit (20) is connected to a master unit (10) 22 and, in combination, the head units (20) and the 23 master unit (10) operate as a single base station 24 using a single carrier.

26 Preferably, cell phone signal interference is 27 reduced both within the first coverage area (40) and 28 between the first coverage area (40) and a second 29 coverage area.

31 Preferably, the first and second coverage areas are 32 indoor and outdoor coverage areas respectively.

:.. I! r' ee.

: le.::: e.

c:e:: .: 2 Preferably, the system employs Code Division 3 Multiple Access (CDMA) based air interface.

5 Preferably, the master unit (10) provides co 6 ordination and control functions to each head unit 7 (20).

9 Preferably, each head unit (20) transmits identical 10 common control downlink channel information.

12 Preferably, both downlink and uplink signals of each 13 head unit (20) are offset in time relative to those 14 of the other head units (20) in the system.

16 Preferably, the timing offsets are controlled such 17 that the earliest arriving signals and latest 18 arriving signals at a User Equipment (UK) (50) 19 within the coverage area have a time offset which is 2 0 less than or equal to the maximum time delay 21 expected by the UE ( 5 0).

23 Preferably, the phase or timing reference for the 24 downlink channels are dedicated pilots.

26 Preferably, the master unit (10) ranks the head 27 units (20) by comparing uplink quality indicators.

29 Preferably, the uplink quality indicators used to 30 rank the head units (20) are the power received 31 and/or signal quality received.

l : ee.::: ce À.:e:: À: 1 Preferably, the master unit (10) routes dedicated 2 downlink channel information to a UE (50) via one or 3 more of the highest ranked head units (20).

5 Preferably, one or more of the head units (20) with 6 the highest ranking independently receive uplink 7 dedicated signals from a UE (50).

9 Preferably, the master unit (10) continuously re 10 ranks the head units (20) as a UE (50) moves through 11 the coverage area ( 40).

13 Preferably, the head units (20) perform downlink 14 channel power control independently of the other 15 head units (20).

17 Preferably, the downlink channel power control at a 18 head unit (20) is optimized in response to the 19 signal strength received from a UE (50) at said head 20 unit (20).

22 Preferably, the head units (20) perform uplink 23 channel power control independently of the other 24 head units (20).

26 Preferably, the uplink channel power control at a 27 head unit (20) is optimized in response to the 28 signal strength received from a UE (50) at said head 29 unit (20).

31 Preferably, PRACH acknowledgement is performed 32 independently at one or more head units (20).

l : tee::: e.

a:.:: .: 1 Preferably, PRACH acknowledgement is performed 2 independently at one or more head units (20).

4 Preferably, two or more head units (20) receive 5 signalling and data traffic from a UE (50) in order 6 to increase signal diversity and thereby improve 7 signal reception.

9 Preferably, uplink data is routed to the master unit 10 (10) via two or more head units (20), the data from 11 each head unit (20) being constructively combined 12 thus reducing its error rate.

14 An embodiment of the present invention will now be 15 described, by way of example only, with reference to 16 the accompanying drawing in which: 18 Fig. 1 shows a schematic of a system for reducing 19 interference relating to indoor cellular radio 20 telecommunication networks.

22 As shown in Fig. 1, there is provided a Master Unit 23 10 connected to a plurality of Head Units 20. The 24 Head Units 20 look similar, in terms of air 25 interference, to cells in a normal cellular 26 deployment. The Master Unit 10 provides co 27 ordination and control functions to the Head Units 28 20. The combination of multiple Head Units 20 and 29 the Master Unit 10 operate as a single "distributed" 30 base station and use a single carrier.

:. t: lo.

I., I,

1 In use, the Master Unit 10 controls the Head Units 2 20 an such a way that the intra-cell interference is 3 reduced, the probability of call dropout is reduced 4 and the inter-cell interference between indoor and 5 outdoor cells is reduced without sacrificing 6 capacity. Each head unit 20 provides a coverage 7 area 30 that is as a subset of the total coverage 8 area 40 of the cell. A UE 50 that is within the 9 total coverage 40 of the cell will also be within 10 the coverage area 30 of one or more of the head 11 units 20.

13 The invention is particularly applicable to CDMA 14 based cellular systems. The following description

15 is specific to UTRAN (both FDD and TDD modes of 16 operation), however it is equally applicable to 17 other air interface standards based upon CDMA. The 18 UTRAN term for base station is "nodeB" and the 19 distributed base station that is the subject of this 20 invention will be referred to in this context as a 21 "distributed nodeB".

23 The time synchronization between head units 20 must 24 be controlled in order to ensure that the signals 25 transmitted by several head units 20 and received at 26 a single UE 50 can be constructively combined at the 27 UE 50. The carrier phase of multiple head units 20 28 cannot be synchronized and so perfectly time-aligned 29 signals may interfere. The minimum resolvable 30 distance between multi-path components at the UE 50 31 is 1 chip period (each chip period is approximately 32 260ns in UTRAN FDD), so signals must be transmitted

ittIet tiled,;; t. t:.:: -: 1 from each head unit 20 at least 1 chip period away 2 from any other head unit's signal. The maximum time 3 offset between head units is determined by the 4 maximum delay spread expected by the UE 30. This 5 small and controlled time offset between head units 6 20 introduces time diversity into both the uplink 7 and downlink paths. To the UE 50, this time 8 diversity appears as delay spread in the downlink 9 channel and the UE's 50 receiver constructively 10 combines the signals.

12 The Head Units 20 are, like normal UTRAN nodeBs, 13 equipped with the ability to receive, process and 14 report uplink signals for UEs 50 transmitting to 15 them. In addition, they also have the ability to 16 receive, process and report signals when they are 17 idle, in order to sense active transmissions which 18 are being handled by nearby base stations. The Head 19 Units 20 do not have standard Tub interfaces and do 20 not implement the NodeB Application Part (NBAP), 21 these functions being provided by the Master Unit 22 10. O&M interfaces are also terminated in the Master 23 Unit 10.

25 All Head Units 20 will transmit the downlink common 26 control channels with the same information content 27 and on the same scrambling and spreading codes. All 28 Head Units 20 will transmit the downlink common 29 pilot channel and synchronization channels with the 30 same data content. This is possible due to the 31 frame timing offsets between the Head Units 20. The 32 resultant signal, as received by the UE 50, will

e: À:. ..:.: 'd: 1 contain a distinct and resolvable multipath ray for 2 each Head Unit 20 that can be received given the 3 location of the UE 50. This improves reception 4 performance due to increased diversity.

6 In UTRAN FDD spreading code and scrambling code 7 identify a dedicated uplink physical connection.

8 Common channel uplink physical connections are 9 similarly identified access signatures. The Master 10 Unit 10 can rank the Head Units 20 in order of 11 proximity to a particular UE 50, based on 12 correlating the uplink measurements from all the 13 Head Units 20 within the UE's 50 identity. There are 14 sufficient codes defined within UTRAN FDD to permit 15 unambiguous identification of all UEs 50 in a 16 distributed nodes. Ranking could be based upon 17 received power, signal to interference ratio, or any 18 other measure of received signal quality.

20 The Head Units 20 operate independently to receive 21 and acknowledge PRACH bursts. In this way the PRACH 22 power can be reduced since the closest Head Unit 20 23 will acknowledge, using AICH, before the UE 50 is 24 forced to increase PRACH power to reach all head 25 units. The master unit 10 will rank the head units 26 20 in order of proximity to the UE 50 based upon the 27 PRACH received power level and other measurements of 28 signal quality such as signal to interference ratio.

30 The Master Unit 10 will route the signalling and 31 data traffic to one or more of the Head Units 20 32 which is closest to the UE 50. More than one Head

ce hi-: À A:.:::

1 Unit 20 may be used to achieve reinforcement of the 2 signal received by the UE 50. Again this is 3 possible due to the timing offsets between the Head 4 Units 20. The resultant signal, as received by the 5 UE 50, will contain a distinct and resolvable 6 multipath ray for each Head Unit 20 that can be 7 received given the location of the UE 50. This 8 improves reception performance due to increased 9 diversity. The UE 50 will be instructed to use 10 dedicated pilots as a phase reference for the 11 channel, thereby avoiding any problems due to the 12 multiple common pilot channels present within the 13 distributed deployment coverage area.

15 Just as the downlink data may be multiply routed, so 16 uplink data may be multiply received. If there are 17 unused radio resources in nearby Head Units 20, they 18 may be tuned to receive uplink data from a nearby UE 19 50. The uplink data so received may be routed to 20 the Master Unit 10, and combined there, to further 21 reduce the error rate in the data.

23 The Head Units 20 will implement downlink dedicated 24 channel power control locally such that all Head 25 Units 20 that receive power up commands from a UE 50 26 will increase their power output for that channel.

27 Uplink power control is the responsibility of the 28 Head Unit 20 deemed to be best placed to serve the 29 UE 50 (that is the Head Unit 20 that is ranked the 30 highest by the Master Unit 10 in terms of proximity 31 to the UE 50).

À ' ' e,,.

À À C

1 For uplink synchronized systems (for example UTRAN 2 TDD 1.28 Mcps option) the time synchronization 3 decisions are the responsibility of the Head Unit 20 4 deemed to be best placed to serve the UE 50.

6 In the case of power control and synchronization 7 commands the Head Units 20 will change the transmit 8 power during a frame to either emphasise or de 9 emphasise a command. A Head Unit 20 that is not 10 responsible for power control or synchronization 11 decisions will have a small or zero code power 12 during the appropriate bits in the frame to de 13 emphasis its command. Conversely, a Head Unit 20 14 that is responsible for power control or 15 synchronization decisions will increase the code 16 power during the appropriate bits in the frame to 17 emphasis its command.

19 As a UE 50 moves through the coverage area, the 20 Master Unit 10 will change the routing of the 21 signalling and data traffic, to maintain the 22 connection with the UE 50, to maximise the traffic 23 the traffic throughput of the network, and to 24 minimise interference with the external network.

26 Thus, unlike a conventional cellular deployment, the 27 UE 50 is not responsible for signal measurements to 28 identify neighbouring Head Units 20 for use in 29 controlling handover, but instead it cannot 30 distinguish between Head Units 20 and it is the 31 responsibility of the distributed nodes (the

r,, '' ' -:

' À 1 combination of Master Unit 10 and Head Units 20) to 2 track each UE 50 through the system.

4 The synchronization channels, common pilot and 5 common control channels can be transmitted at a 6 lower power because they are transmitted by multiple 7 Head Units 20 within the system and the mean path 8 loss between the UE 50 and nodes will be reduced. In 9 this way the interference with the external macro 10 network is reduced.

12 It will be appreciated that a UE 50 moving within 13 the network of Head Units 20 will receive time 14 delayed copies of the data from each Head Unit 20, 15 but that the UE 50 will treat these as multi-path 16 copies and reconstruct them in the usual manner.

17 The UE 50 will therefore see the network of Head 18 Units 20 as a single cell and the receive 19 performance will improve due to diversity gain.

21 The use of local power control and small cell size 22 will reduce the required power output on any 23 specific code channel to achieve a given quality of 24 service. In this way the intra-cell interference is 2 5 reduced.

27 The problems associated with call dropout due to 28 inter-cell interference at cell boundaries is not 29 present within the distributed nodes coverage area 30 as described in this invention. All Head Units 20 31 transmit complementary signals that combine 32 constructively. This is a consequence of the fact

He t: t' c-:e..

:e c:: 1 that all Head Units 20 are seen from a UE 50 2 perspective as a single nodeB.

4 Modifications and improvements may be made to the 5 above without departing from the scope of the 6 present invention.

Claims

|e:. ce:.

1 CLAIMS

3 1. A cellular radio telecommunication system for 4 reducing cell phone signal interference in a 5 cellular radio telecommunication network, said 6 system comprising a plurality of head units (20) 7 spatially separated throughout a first coverage area 8 (40), wherein each head unit (20) is connected to a 9 master unit (10) and, in combination, the head units 10 (20) and the master unit (10) operate as a single 11 base station using a single carrier.

13

2. A system as claimed in claim 1 wherein cell 14 phone signal interference is reduced both within the 15 first coverage area (40) and between the first 16 coverage area (40) and a second coverage area.

18

3. A system as claimed in claim 2 wherein the 19 first and second coverage areas are indoor and 20 outdoor coverage areas respectively.

22

4. A system as claimed in any preceding claim 23 wherein the cellular radio telecommunication system 24 employs Code Division Multiple Access (CDMA) based 25 air interface.

27

5. A system as claimed in any preceding claim 28 wherein the master unit (10) provides co-ordination 29 and control functions to each head unit (20).

1

6. A system as claimed in any preceding claim 2 wherein each head unit (20) transmits identical 3 common control downlink channel information.

5

7. A system as claimed in any preceding claim 6 wherein both downlink and uplink signals of each 7 head unit (20) are offset in time relative to those 8 of the other head units (20) in the system.

10

8. A system as claimed in claim 7 wherein the 11 timing offsets are controlled such that the earliest 12 arriving signals and latest arriving signals at a 13 User Equipment (UK) (50) within the coverage area 14 have a time offset which is less than or equal to 15 the maximum time delay expected by the UE (50).

17 8. A system as claimed in claims 7 or 8 wherein 18 the phase or timing reference for the downlink 19 channels are dedicated pilots.

21

9. A system as claimed in any preceding claim 22 wherein the master unit (10) ranks the head units 23 (20) by comparing uplink quality indicators.

25

10. A system as claimed in claim 9 wherein the 26 uplink quality indicators used to rank the head 27 units (20) are the power received and/or signal 28 quality received.

30

11. A system as claimed in any of claims 9 or 10 31 wherein the master unit (10) routes dedicated

A:::;'

À c:e c.:.:: 1 downlink channel information to a UE (50) via one or 2 more of the highest ranked head units (20).

4

12. A system as claimed in any of claims 9 to 11 5 wherein one or more of the head units (20) with the 6 highest ranking independently receive uplink 7 dedicated signals from a UE (50).

9

13. A system as claimed in any of claims 9 to 12 10 wherein the master unit (10) continuously re-ranks 11 the head units (20) as a UE (50) moves through the 12 coverage area (40).

14

14. A system as claimed in any preceding claim 15 wherein the head units (20) perform downlink channel 16 power control independently of the other head units 17 (20).

19

15. A system as claimed in claim 14 wherein the 20 downlink channel power control at a head unit (20) 21 is optimised in response to the signal strength 22 received from a UE (50) at said head unit (20).

24

16. A system as claimed in any preceding claim 25 wherein the head units (20) perform uplink channel 26 power control independently of the other head units 27 (20).

29

17. A system as claimed in claim 16 wherein the 30 uplink channel power control at a head unit (20) is 31 optimised in response to the signal strength 32 received from a UE (50) at said head unit (20).

ee.:e Hi. seeec:-

2

18. A system as claimed in any preceding claim 3 wherein PRACH acknowledgement is performed 4 independently at one or more head units (20).

6

19. A system as claimed in any preceding claim 7 wherein two or more head units (20) receive 8 signalling and data traffic from a US (50) in order 9 to increase signal diversity and thereby improve 10 signal reception.

12

20. A system as claimed in any preceding claim 13 wherein, uplink data is routed to the master unit 14 (10) via two or more head units (20), the data from 15 each head unit (20) being constructively combined 16 thus reducing its error rate.