WO2001037590A1

WO2001037590A1 - A wireless baseband relay for improving the performance of digital cellular systems

Info

Publication number: WO2001037590A1
Application number: PCT/AU2000/001412
Authority: WO
Inventors: Dong Jye Shyy; Christopher A. Isaac
Original assignee: Prescient Networks Pty Ltd
Priority date: 1999-11-18
Filing date: 2000-11-20
Publication date: 2001-05-25
Also published as: AUPQ412999A0

Abstract

A wireless baseband relay (10) which acts as an intermediate stationary multiplexing/demultiplexing gateway between a base station (BS) and mobile stations (MSs). A plurality of MS baseband processors (12) for communicating with a base station (13) are provided in the relay (10), and a plurality of BS baseband processors (14) are operatively connected to the MS processors (12) for communicating with the mobile stations (15). There is one BS baseband processor (14) for each mobile station (15). A performance optimisation processor (26) is provided for optimising the performance of the communications link between the relay (10) and the MSs (15). Upper layer control processors (24) perform all upper layers processing for the MS baseband processors (12) and the BS baseband processors (14). Performance optimisation processor (26) instructs the upper layer processors (24) to distinguish packet-switched connections from other types of connections. For packet-switched connections, a multiplexing function is performed for the connections from the MSs to the serving BS, and a demultiplexing function is performed for the connections from the serving BS to the MSs. The relay (10) advantageously shields the BS (13) from the mobility of the MSs (15).

Description

A WIRELESS BASEBAND RELAY FOR IMPROVING THE PERFORMANCE OF DIGITAL CELLULAR SYSTEMS

FIELD OF THE INVENTION

The invention is in the field of mobile communications. It relates to a baseband relay for enhancing the performance of digital cellular networks. It has applications in the areas of mobile communications and wireless data communications for second, third and fourth generations digital cellular/personal communications services.

BACKGROUND OF THE INVENTION

Mobile communication services are evolving from second generation (2G) voice and low-data-rate services (~64 kbps) to third generation (3G) high-data-rate services (~1 Mbps). These high-data-rate services are typically performed in an indoor environment. However, the coverage range for high-data-rate services is inherently smaller than that for voice or low-data-rate services due to a more stringent C/I requirement. To extend the coverage range of high-data-rate services, a baseband relay is proposed to be used. In addition to the range extension, the baseband relay may also perform multiplexing of the packet-switched traffic under its coverage. The result is a local multipoint distribution system (LMDS)-like pipe between the base station (BS) and the baseband relay. The BS is also shielded from the mobile effect by the relay.

A variety of prior art protocols, techniques and architectures have been proposed for extending the coverage range of high-data-rate services. For example, US 5,974,236 describes a dynamically reconfigurable communications network in which each node is able to take the role of an origination node, a destination node or a repeater node. The node can be mobile or stationary. A received message in a node A is routed to the next node B based on the destination of the message and the routing tables stored in node A. The routing table is constantly updated and self-reconfigured based on the availability of the link between nodes. In a similar vein, US 5,930,297 and 5,625,653 describe a base station emulator which is basically a subscriber station with additional _ _

capability such as initiating synchronisation and processing the messages from other subscribers. The base station emulator can be used as a repeater to enhance the coverage range.

These types of prior art scheme fall into the category of the opportunity driven multiple access (ODMA) scheme recently introduced in the Third Generation Partnership Project (3GPP) standards. That is to say, a mobile can use other mobiles or repeaters in the network to relay its message to the final destination (the BS). The result is that the range of a mobile (for high-data-rate services) is extended. By contrast, in the present invention, although the range of high-data-rate services can also be enhanced, packet-switched traffic is typically multiplexed into a multiplexed stream to achieve higher spectral efficiency and shield the base station from the mobility effect.

A variety of schemes that employ radio frequency (RF) repeaters to extend the coverage range are described in US 5,953,637; 5,970,410, 5,930,240; 5,527,376; and 5,449,395; and, WO 98/29962. However, the present invention does not employ a RF repeater, but is based on the use of a baseband relay that demodulates/remodulates the transmission signal. Furthermore, unlike these prior art schemes, the present invention typically performs multiplexing on packet-switched traffic and shields the base station from the mobility of the mobile stations/user equipment.

SUMMARY OF THE INVENTION

Throughout this specification the term "comprising" is used inclusively, in the sense that there may be other features and/or steps included in the invention not expressly defined or comprehended in the features or steps subsequently defined or described. What such other features and/or steps may include will be apparent from the specification read as a whole.

According to one aspect of the present invention there is provided a wireless baseband relay for improving the performance of digital cellular systems, the relay comprising:

a mobile station (MS) processor for communicating with a base station; and a plurality of base station (BS) processors operatively connected to said MS processor for communicating with a plurality of mobile stations, wherein the relay acts as an intermediate stationary gateway between said base station and said plurality of mobile stations.

Preferably the relay further comprises a performance optimisation processor operatively connected to said MS processor and said plurality of BS processors for optimising the performance of the communications link between the relay and the mobile stations. Preferably the relay also comprises an upper layer control processor connected between said MS processor and said plurality of BS processors, for performing all upper layer processing for said BS and MS processors, said upper layer control processor also being operatively connected to said performance optimisation processor.

Preferably said MS processor is one of a plurality of MS processors, a separate MS processor being provided for each voice or circuit-switched connection and a single MS processor being provided for multiple packet-switched connections.

Preferably the relay employs two sets of antennas, a first set for communicating with one or more serving base stations and a second set for communicating with the mobile stations. Each set of antennas can be omnidirectional, directional, an antenna array and/or a distributed antenna.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to facilitate a more detailed understanding of the nature of the invention a preferred embodiment of the wireless baseband relay will now be described in detail, by way of example, only, with reference to the accompanying drawings, in which:

Figure 1 is a functional block diagram of a preferred embodiment of the baseband relay in accordance with the present invention; and, Figure 2 illustrates schematically a typical configuration of the baseband relay in a mobile communications network.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

In its preferred form this invention uses a wireless baseband relay as an intermediate stationary multiplexing/demultiplexing gateway between a base station (BS) and mobile stations (MSs)/user equipment (UE). There are MS/UE processors in the relay for communicating with the serving BS . The relay also has BS processors typically performing modulation/demodulation, spreading/despreading and coding/decoding to communication with the MSs.

This invention is applicable to all digital cellular standards: time division multiple access (TDMA) and code division multiple access (CDMA) as well as time division duplex (TDD) and frequency division duplex FDD) modes; however, CDMA (including Wideband-CDMA) is used as a representative standard in the following description by way of example.

A functional block diagram of a preferred embodiment of a baseband relay 10 is depicted in Figure 1. The baseband relay 10 comprises a plurality of mobile station (MS) baseband processors 12 for communicating with a base station 13 (see Figure 2) and a plurality of base station (BS) baseband processors 14 operatively connected to said MS processors 12 for communicating with a plurality of mobile stations 15 (see Figure 2). The relay 10 effectively acts as an intermediate stationary gateway between the base station 13 and the plurality of mobile stations 15. There is typically a plurality of MS baseband processors 12 respectively for each voice or circuit- switched connection 16, and typically one MS baseband processor 12 for multiple packet-switched connections 18. Each MS baseband processor 12 handles both dedicated traffic and control channels. A CDMA common control channel processor 20 handles pilot, paging and sync channels.

The BS baseband processors 14 are used to communicate with the MSs/UE. There is one BS baseband processor 14 for each MS/UE. Each BS baseband processor 14 handles both dedicated traffic and control channels. The CDMA common control channel processor 22 handles pilot, paging, and sync channels. Upper layer control processors 24 are provided connected between the BS processor 14 and the MS processors 12. Upper layers in the communications link include the Media Access Control (MAC) layer, the Radio Link Control (RLC) layer and the Control (RRC) layer. The MAC/RLC/RRC processors 24 perform all upper layers processing for the MS baseband processors and BS baseband processors.

A performance optimisation processor 26 is provided for optimising the performance of the link between the baseband relay and the MSs/UE by instructing the BS processors 14 and MAC/RLC/RRC processors 24 to perform various tasks. For example, performance optimisation processor 26 instructs the MAC/RLC/RRC processors 24 to distinguish packet-switched connections from other types of connections. For packet-switched connections, a multiplexing function is performed for the connections from MSs/UE to serving BS and a demultiplexing function is performed for the connections from serving BS to MSs/UE. It is also responsible for the mapping between the logical channel ID and the mobile user ID (or mobile directory number).

The performance optimisation processor 26 may also, for example, instruct the BS baseband processor to selectively amplify high-data-rate channels based on the spreading factor. It may also instruct the CDMA common control channel processor to adapt its pilot power to the environment such that the pilot pollution is eliminated and the channel estimation performance at MSs/UE is improved. The performance optimisation processor can enhance the MAC/RLC/RRC processor performance for the link between serving BS and relay as well as the link between the relay and the MSs/UE.

Intermediate (IF) and radio (RF) frequency subsystems 28,30 are also provided in the relay for facilitating the transmission/reception of RF signals from to the base station and the MSs/UE respectively.

Two sets of antennas need to be deployed on the relay (as shown in Figure 2). One set of antennas 32 is used between the relay and the serving BS 13 (antenna set 1). The other set of antennas 34 is used between the relay and the MSs/UE 15 (antenna set 2). Each set of antennas can be omni-directional, directional, antenna array, and/or distributed antenna.

There are two options for the relay for treating the common control channels from the serving BSs.

A first option is that the relay 10 is an extension of the serving BS 13. In this case, the relay does not reintroduce new common control channels. That is to say pilot, sync and paging channels pass through the relay transparently. With the delay element introduced by the relay, the serving BS 13 is able to identify whether the mobiles 15 are under relay coverage or not.

A second option is that the relay is a picocell in the system. In this case, the baseband relay 10 terminates all common control channels (except paging channels) and reintroduces them for the mobiles. For example, the relay does not use a common pilot channel on the forward link. Instead, the relay uses an auxiliary pilot channel. However, in this case, handoff is required for a mobile to move from the coverage of the relay to that of the BS 13 and vice versa. The relay also needs to introduce its own sync channel. This option is more complicated because (a) the base station controller/radio network controller (BSC/RNC) needs to treat the relay as an entity in its configuration database, and (b) handoff needs to be implemented between the relay and the serving BS. In the following discussion, the first option is assumed.

Although the common control channels pass through the relay transparently, some enhancements can be made to improve the performance of the links between the relay 10 and the MSs 15 without violating the standards of CDMA. (Note that the paging channel passes through the relay transparently. The paging message is addressed to an individual mobile, not to the relay). For example, the setting of pilot power and the configuration of antenna array/distributed antenna (antenna set 2) can be optimised for a particular in-building environment to eliminate excessive overlapping pilot channel coverage. The result is a decrease in downlink interference. Another example is to increase the pilot channel power to facilitate better channel estimation for the traffic channels, and the result is the requirement for energy per bit/interference density (Eb/Nt) set point or signal to interference ratio (SIR) set point on the traffic channels can be reduced.

All initial accesses of the MSs/UE 15 under the coverage of the relay will go through the relay by definition. The initial access procedure follows the CDMA standards. Depending on whether a connection has been set up, the relay treats the initial access requests differently. When there is no existing connection between the relay and the BS, the relay uses an uplink random access channel to send the initial access request for the mobile. Once a traffic channel has been established between the BS and the relay, the relay can use in-band signalling either (a) to send initial access requests to the BS and let the BS interpret the requests, or (b) interpret the request locally and ask for additional resource from the BS based on the interpretation. The number of CDMA uplink traffic channels between the BS and relay is optimised to provide the best spectral efficiency. For voice channels and circuit-switched channels, since the user is likely to travel from the coverage area of the relay to that of the serving BS frequently, these channels are set up individually between the relay and the BS. Note that the voice and circuit-switched channels from the same user can be multiplexed onto the same physical channel with different transport formats. In this case, there is no need to separate them into two connections. Only one mobile baseband processor is needed.

For packet-switched channels, the relay multiplexes all incoming traffic from MSs into one (or more) physical uplink CDMA channels. The multiplexing of incoming traffic at the relay is done at the media access control (MAC) layer where each connection is assigned a dedicated logical channel ID. (A logical channel ID is mapped to a mobile user ID or mobile directory number). The MAC layer maps one or more than one logical channel to one transport channel depending on the QOS requirements of the logical channels. Transport channels are the services offered by the physical layer to the MAC layer. Transport channels are further multiplexed into one or more physical channels. By the same token, the serving BS also multiplexes all traffic destined to the mobiles under the coverage of baseband relay into one (or more) physical uplink CDMA channels. The baseband relay further demultiplexes one downlink physical channel into multiple logical channels and then remodulates each logical channel into a physical channel for each mobile. The data rate of the uplink physical CDMA channels varies based on the incoming traffic load from the MSs. By the same token, the data rate of the downlink physical CDMA channels also varies based on the incoming traffic. (In CDMA, bandwidth of the channel can be changed, for example, by varying the spreading factor of the CDMA channel). However, once the mobile moves out of the coverage area of the relay, the mobile cannot decode the multiplexed signal directly. In this case, the connection for the mobile will be dropped. It is conjectured that packet-switched applications (such as Internet browsing) are mostly performed while the user is stationary or in low mobility. Hence, we do not perceive this to be a significant issue.

Note that although physically the BS thinks that it is communicating with the relay directly, logically the BS is communicating with all MSs under the coverage of the relay.

When the relay detects high-data-rate channels, the relay will amplify high-data rate traffic channels such that their coverage range can be extended. However, the relay will not amplify the low-data-rate traffic channels. The relay can be either notified by the BS or configured via local management console about what the minimum data rate needs to be for the high-data-rate channels. The other possibility is that the relay can estimate the following: Under what condition a CDMA channel needs to be amplified in order for the CDMA channel to have the desired coverage? For example, the relay can estimate what is the maximal spreading factor (Max SF) a channel needs to use for reaching the desired area. If the SF of the channel is less than the Max SF, the channel is amplified. Note that the spreading factor may be dynamically adapted based on the interference situation.

When the antenna 1 deploys an antenna array, the antenna array can be used to perform load balancing among BSs. For example, initially, the antenna array is used to form a beam pointing to BS A. However, when BS A is overloaded with traffic, the antenna array can rotate the beam from point to BS A to BS B. Each BS is associated with two thresholds for the traffic load. The upper load is the threshold where the relay should not use the BS as serving BS if the BS traffic load is above the upper load. The lower load is the threshold where a BS is qualified as a candidate to be a serving BS if the BS traffic load is below the lower load.

In some cases, it is also possible to configure the antenna array to form more than one beam and each beam points to a different BS . This scenario is useful when the traffic load under the relay is larger than one BS can handle. Clearly, the relay will not combine the signals of BS A and BS B and send them to the same area. Instead, the relay will route BS A signals to an area which is disjoint from that for BS B signals.

As discussed earlier, a distributed antenna technique can be used to extend the coverage of the baseband relay to where the remote antenna is located . The connection between the baseband relay and remote antenna can be wired or wireless backhaul. Two of the criteria for implementing a wireless backhaul is that it should not interfere with the cellular/PCS band and it has enough bandwidth to transport a 3G signal. For example, 5 GHz wireless LAN is a good candidate for implementing the wireless backhaul since its bit rate can reach 54 Mbit/sec and it does not interfere with 2G or 3G bands.

Now that a preferred embodiment of the baseband relay has been described in detail, it will be apparent that the baseband relay provides a number of advantages in digital mobile cellular communication systems, including the following:

• Higher spectral efficiency (b/s/Hz)

• Lower Eb/Nt set point for both uplink and downlink traffic channels because the relay appears to be stationary to the BS. In other words, the relay shields the mobility effects from the BS (Higher capacity)

• High trunking efficiency for the packet-switched multiplexed channel between BS and relay (Higher capacity)

• Elimination of soft and softer handoff for the mobiles under the relay by appropriately tuning the antenna configurations of the relay (Higher capacity)

• Relaxation of the power control update interval for the links between BS and relay

• The loading at the BS can be set higher since the stability of the power control is higher and the capacity is largely increased (Higher capacity) • Increased frequency re-use (Higher capacity)

• Increased sectorisation gain (Higher capacity)

• Lower average transmit power from mobiles (Higher capacity)

• Diversity gain and code reuse from antenna array and distribution antenna deployment (Higher capacity)

• Selective performance optimisation based on the channel characteristics and environment

• Increased range for high-data-rate connections only (Better Coverage and Quality of Service) • Eliminate pilot pollution

• Enhance channel estimation by increasing pilot power

• It allows the wireless operators to deploy earlier and cheaper as well as extend coverage without extra BSs

• Wireless backhaul allows the wireless operators to have easy installation and reconfiguration of remote antennas

In addition to the above advantages, the transmission control protocol/Internet protocol (TCP/IP), radio link protocol (RLP) and media access control (MAC) layers can also be optimised between the BS and the relay as well as between the relay and the mobiles. The overall performance is further improved. Also, compression can be deployed between the BS and mobile processor of the baseband relay to further increase the spectral efficiency.

When the antenna set 2 employs an antenna array and/or distributed antenna, spatial signalling processing can be performed on the relay such as transmit and receive diversity as well as code reuse. The other advantage of spatial signalling processing is that the other cell interference can be reduced due to the directionality of the beam formed by the antenna array.

It will be apparent to persons skilled in the digital cellular communications arts that numerous variations and modifications may be made to the described baseband relay, in addition to those already described, without departing from the basic inventive concepts. All such variations and modifications are to be considered within the scope 01/37590 _ _n _ PCT/AUOO/01412

of the present invention, the nature of which is to be determined from the foregoing description and the appended claims.

Claims

_ 12 _THE CLAIMS DEFINING THE INVENTION

1. A wireless baseband relay for improving the performance of digital cellular systems, the relay comprising:

a mobile station (MS) processor for communicating with a base station; and

a plurality of base station (BS) processors operatively connected to said MS processor for communicating with a plurality of mobile stations, wherein the relay acts as an intermediate stationary gateway between said base station and said plurality of mobile stations.

2. A wireless baseband relay as defined in claim 1, wherein the relay further comprises a performance optimisation processor operatively connected to said MS processor and said plurality of BS processors for optimising the performance of the communications link between the relay and the mobile stations.

3. A wireless baseband relay as defined in claim 2, wherein the relay further comprises an upper layer control processor connected to said MS processor and said plurality of BS processors, for performing all upper layer processing for said BS and MS processors, said upper layer control processor also being operatively connected to said performance optimisation processor.

4. A wireless baseband relay as defined in claim 3, wherein said performance optimisation processor instructs said upper layer control processor to distinguish packet-switched connections from other types of connections, and to perform a multiplexing/demultiplexing function for said packet-switched connections.

5. A wireless baseband relay as defined in claim 4, wherein said performance optimisation processor instructs said BS processors to selectively amplify high-data- rate channels based on the spreading factor.

6. A wireless baseband relay as defined in claim 2, wherein said MS processor is one of a plurality of MS processors WO 01/37590 _ ₁₃ _ PCT/AUOO/01412

7. A wireless baseband relay as defined in claim 6, wherein a separate MS processor is provided for each voice or circuit-switched connection and a single MS processor is provided for multiple packet-switched connections.

8. A wireless baseband relay as defined in claim 8, wherein the relay employs two sets of antennas, a first set for communicating with one or more serving base stations and a second set for communicating with the mobile stations.

9. A wireless baseband relay as defined in claim 2, wherein the relay is adapted to operate in accordance with a code division multiple access (CDMA) digital cellular transmission standard.

10. A wireless baseband relay as defined in claim 9, wherein the relay further comprises a BS CDMA common control channel processor and a MS CDMA common control channel processor for handling pilot, paging and sync channels.

11. A wireless baseband relay as defined in claim 10, wherein said performance optimisation processor instructs the BS CDMA common control channel processor to adapt its pilot power to the environment such that pilot pollution is eliminated and the channel estimation performance at the MSs is improved.

12. A wireless baseband relay as defined in claim 11, wherein said performance optimisation processor instructs the BS CDMA common control channel processor to set its pilot power and to configure an antenna set to be optimised for a particular in- building environment to eliminate excessive overlapping pilot channel coverage.

13. A wireless baseband relay as defined in claim 10, wherein said performance optimisation processor instructs MAC/RLC/RRC processors to optimise the transmission control protocol/Internet protocol (TCP/IP), the RLP and MAC layers between the BS and the relay as well as between the relay and the mobile stations.

14. A wireless baseband relay as defined in claim 10, wherein said performance optimisation processor instructs the MS processor to perform compression such that O 01/37590 _ ₁₄ _ PCT/AUOO/01412

compression can be deployed between the BS and MS mobile processor of the relay, and the spectral efficiency is further improved.