Литература / UMTS-Report

Figure 2. Histogram for needed transmissions per hybrid II ARQ packet. Both Q-O-QAM and B-O- QAM packet are included.

7.7.3.1.2 Speech

The simulated capacity is 190 kbps/MHz/cell. Then the blocking and dropping are ca. 0 and bad quality is ca. 2 %. Thus quality requirements are fulfilled with that loading. An user uses in average 1.12 slots per frame when it is active. The developed fractional cell loading was 65 % in the six middle cells. The used power dynamics was 30 dB.

With micro cell speech simulations the matrix was 16 time slots x 9 frequencies. In reality the number of time slots would be 64. Only 16 time slots were used in order to reduce simulation time. Thus less diversity is obtained and more blocking happens which leads to that the simulated capacity becomes lower than with the full channel matrix.

7.7.3.2 Indoor

7.7.3.2.1 UDD2048

The simulated spectrum efficiency is 332 kbps/MHz/cell. Of all sessions 98.4 % fulfill quality criteria. If all bits user requests during a session are received correctly within 150 ms, the user is regarded as satisfied user independent of active bit rate. Insufficient active session throughput is the limiting reason for most sessions not fulfilling the performance criteria.

The average active session throughput is 713 kbps and 0.4 % of the sessions have active session throughput 2048 kbps or higher. If offered load is reduced the average active session throughput and ratio of the users having active session throughput 2048 kbps or higher increases. Reuse 1 is used with fractional load of 48%. The distribution of active session throughputs can be seen in Figure 3. In Figure 4 histogram for needed transmissions per a hybrid II ARQ packet is presented.

With pico cell UDD2048 simulations the channel matrix was 16 time slots x 9 frequencies. The preferred modulation is Q-O-QAM, but the modulation is switched to B-O-QAM if offer traffic does not require Q-O-QAM. If the BTS buffer has less bits that can be transmitted in a one radio packet, the radio packet is filled with dummy bits. These overhead dummy bits are not included into spectrum efficiency nor into active session throughput. The dynamic range of the power control is 30 dB.

UDD2048 simulation without walls presented in this paper, expect it has additional wall attenuation of 5 dB and standard deviation of slow fading is reduced from 12 dB to 4 dB.

The simulated spectrum efficiency is 743 kbps/MHz/cell. Of all sessions 98.7 % fulfill quality criteria. If all bits user requests during a session are received correctly within 150 ms, the user is regarded as satisfied user independent of active bit rate. Insufficient active session throughput is the limiting reason for most sessions not fulfilling the performance criteria.

The average active session throughput is 692 kbps and 0.4 % of the sessions have active session throughput 2048 kbps or higher. If offered load is reduced the average active session throughput and ratio of the users having active session throughput 2048 kbps or higher increases. Reuse 1 is used with fractional load of 86 %. The distribution of active session throughputs can be seen in Figure 5. In Figure 6 histogram for needed transmissions per a hybrid II ARQ packet is presented.

With pico cell UDD2048 simulations the channel matrix was 16 time slots x 8 frequencies. The preferred modulation is Q-O-QAM, but the modulation is switched to B-O-QAM if offer traffic does not require Q-O-QAM. If the BTS buffer has less bits that can be transmitted in a one radio packet, the radio packet is filled with dummy bits. These overhead dummy bits are not included into spectrum efficiency nor into active session throughput. The dynamic range of the power control is 30 dB.

Figure 5. Histogram for session throughputs.

Figure 6. Histogram for needed transmissions per hybrid II ARQ packet. Both Q-O-QAM and B-O- QAM packet are included.

7.7.3.3 Macro cell

7.7.3.3.1 Speech

The simulated capacity is 55 kbps/MHz/cell. Then the blocking and dropping is less than 1 % and bad quality is less than 1 %. Thus quality requirements are fulfilled with that loading. An user uses in average 1.48 slots per frame when it is active. The average fractional cell loading was 72 % in the middle cells. The used power dynamics was 10 dB.

With macro cell speech simulations the matrix was 16 time slots x 3 frequencies, which indicates reuse 1/3. In reality the number of time slots would be 64. Only 16 time slots is used in order to reduce simulation time. Thus less diversity is obtained and more blocking happens which leads to that the simulated capacity becomes lower than with the full channel matrix.

7.7.3.3.2 LCD384

The simulated capacity is 113 kbps/MHz/cell. In this simulation 98,1% of all users are satisfied, thus quality requirements are fulfilled with this loading. The used modulation is B-O-QAM and available link adaptation modes are 6/16, 8/16 and 12/16. With macro cell LCD384 simulations the matrix is 16 time slots x 9 frequencies, which indicates reuse 1/1. The average fractional cell loading is ca. 28 % in the middle cells. During the simulation, the ratio link adaptation modes (6/16, 8/16 and 12/16) were 11%, 36% and 52%, respectively.

7.7.4 Discussion

System simulation results for WB-TDMA are shown. The used RRM scheme is based on the interference averaging principle. In order to study the effects of fast algorithms such as ARQ and Frequency hopping, the interface between link and system level results is implemented according to [2].

The results present a lower bound case due to several reasons: downlink results are presented, all the possible enhancements by the interference averaging radio resource management algorithms are not implemented and network parameter optimization is not completed.

These simulations have been done with FDD assumption. To some extent these results can be generalized to show the trends also for the TDD mode. Detailed TDD simulations would be needed to evaluate the TDD specific features such as flexibility for resource allocation in upand downlink and

utilization of asymmetric spectrum allocations. Also the link level results for TDD may be enhanced due to algorithms that make us of reciprocity of the channel.

The future improvements to be tested include several things. Among these are interference cancellation, antenna diversity, antenna diversity, the application of ARQ to LCD data, better coding schemes (e.g. increased constraint length, optimal puncturing and concatenated codes), optimized mapping of user data into packets, fast power control and channel allocation to cells.

Future work will include the estimation of signaling overhead and degradation of the obtained capacity due to signaling. The estimated signaling load is less than 10 % of the capacity. This load has not been subtracted from the presented capacity figures.

The obtained simulation results show high capacity for the WB-TDMA system especially for UDD services. Main conclusions are:

∙WB-TDMA with interference averaging is very promising alternative especially for non delay sensitive packet services.

∙High capacities can be provided without extensive frequency and network management

∙Since WB-TDMA has hardly any intra cell interference and reuse 1 can be applied, additional inter cell interference management and reduction techniques, such as adaptive antennas, joint detection and cell planning can still increase the capacity.

∙For RT services the possible gains of faster quality based power control should be investigated.

7.8 REFERENCES

[1]UMTS 30.03 v3.0.0 “Selection procedure for the choice of radio technologies of UMTS”, Annex 2

[2]ETSI SMG2 UMTS ad hoc #3 TDoc 73, Rennes, 1997.

[3]ETSI SMG2 Gamma Concept Group, TDoc G18/97, Sollentuna, 1997.

[4]ETSI SMG2 Gamma Concept Group, TDoc /97, Bad Salzderfurth, 1997.

8. High Level Requirements

This section describes how the W-TDMA concept meets the High Level Requirements for UTRA. Boxed text from ETR 04-01 has been included for reference.

Some issues are identified for further study by Gamma Group. Others may be more appropriate for consideration by SMG2 during later stages of UMTS standardisation.

8.1 Bearer capabilities

8.1.1 Maximum user bit rate

The UTRA should support a range of maximum user bit rates that depend upon a users current environment as follows:

Rural Outdoor: at least 144 kbit/s (goal to achieve 384 kbit/s), maximum speed: 500 km/h

Suburban Outdoor: at least 384 kbps (goal to achieve 512 kbit/s), maximum speed: 120 km/h

Indoor/Low range outdoor: at least 2Mbps, maximum speed: 10 km/h

It is desirable that the definition of UTRA should allow evolution to higher bit rates.

-Rural Outdoor: 144kbps will be available throughout the operator’s service area. The radio interface can tolerate the Doppler spread and rapidly changing channel characteristics associated with high speed vehicles (up to at least 1500km/h with 1/64 slot bursts). The maximum cell size depends on propagation conditions, but is comparable with GSM (assuming similar requirements for bearer capabilities and quality of service).

-Suburban Outdoor: 384kbps rate will be available with complete coverage of a suburban or urban area

-Indoor/Low range outdoor: 2Mbps will be available indoors and over localised coverage outdoors

The maximum practical bit rate which can be provided depends on factors such as the operating environment, required quality of service, traffic loading and proximity of mobile to base station.. However, the radio interface can support rates up to around 1Mbps for Rural and Suburban Outdoor, and 4Mbps over short ranges.

8.1.1.1 Bearer Service Attributes

The W-TDMA concept can provide bearers with the necessary attributes. i.e. different connection modes, symmetry, communication configuration, information transfer rate, delay variation, maximum transfer delay, maximum bit error rate, error characteristics.

8.1.2 Flexibility

Negotiation of bearer service attributes (bearer type, bit rate, delay, BER, up/down link symmetry, protection including none or unequal protection),

parallel bearer services (service mix), real-time / non-real-time communication modes, adaptation of bearer service bit rate

Circuit switched and packet oriented bearers

Supports scheduling (and pre-emption) of bearers (including control bearers) according to priority

Adaptivity of link to quality, traffic and network load, and radio conditions (in order to optimise the link in different environments).

Wide range of bit rates should be supported with sufficient granularity

Variable bit rate real time capabilities should be provided.

Bearer services appropriate for speech shall be provided.

The W-TDMA concept provides flexibility of bearer service attributes by use of a number of different transmission bursts optimised for different bit rates in different radio environments. The Link Adaptation mechanism can be used to dynamically maintain the quality of the connection under changes in propagation and interference conditions by adjusting transmission format and number of slots allocated.

Bit rate granularity is achieved primarily by allocating different numbers of transmission slots, but this can be suplemented if necessary by adjusting channel coding rates.

Parallel bearers can be transmitted independently, or where appropriate by multiplexing together into a single channel.

Circuit switched and packet oriented services are supported efficiently by Real-Time and Non-Real- Time bearer concepts.

Variable rate data services are supported by dynamically changing the capacity allocation.

Scheduling of bearers is allowed, but could be the subject of further study by SMG2.

Bearers optimised for speech are available.

The bearer service attributes can be configured as required on initiation of a service, and changed dynamically if required.

8.1.2.1 Minimum bearer capabilities

The following table shows the potential combinations for the most important characterisation attributes (based on ETR-04-01).

8.1.3 Configuration management

W-TDMA will allow the definition of configuration management features.

8.1.4 Evolution and modularity

The W-TDMA concept is service independent, and is defined so that UMTS can be implemented in phases with enhancements for increasing functionality (for example making use of different modulation and coding technology). The requirement for backwards compatibility can be met by provision of a negotiation mechanism to agree on supported capabilities between mobiles and infrastructure.

The W-TDMA concept is consistent with the requirements of an open modular architecture and implementation of software downloading of radio interface features. However these aspects require further development within SMG2.

8.1.5 Handover

Provide seamless ( to user ) handover between cells of one operator.

The UTRA should not prevent seamless HO between different operators or access networks.

Efficient handover between UMTS and 2nd generation systems, e.g. GSM, should be possible.

8.1.5.1 Overall handover requirements

Efficient seamless (mobile assisted) handovers can be provided in networks with synchronised base stations and between TDD and FDD systems. Seamless handover between unsynchronised systems, is for further study by Gamma Group.

Signalling load from handovers is not expected to be significant but is dependent on scenario, and could be the subject of further study by Gamma Group.

The level of security is not be affected by handovers. Security in general is ffor further study in SMG2.

Handover to second generation systems can be supported by use of an idle frame allowing measurements of signal strengths from alternative base stations.

The choice of frame structure allows synchronisation of UTRA with GSM sharing the same cell sites which simplifies handover in this case.

8.1.5.2 Handover requirements with respect to the radio operating environments

The W-TDMA radio interface allows handovers within a network, between different environments and between networks run by different operators.

8.2 Operational requirements

8.2.1 Compatibility with services provided by present core networks

ATM bearer services

GSM services

IP (Internet Protocol) based services

ISDN services

Flexible RT and NRT bearers with a range of bit rates etc., allow current core network services to be supported.