Литература / UMTS-Report

Table 9: Modulation/coding schemes (LCD 144, Pedestrian A)

With re-use pattern 3 the average number of slots per channel is 1.33, which gives 11 effective channels per carrier, and a capacity of 23 Erlangs per cell or 230kbps/MHz/Cell with a fractional loading of 70%. With adjacent cell re-use the average number of slots is 3.1, which gives 4 effective channels per carrier, and a capacity of 25 Erlangs per cell or 250kbps/MHz/Cell with fractional loading of 60%.

These figures may be optimistic since the number of effective channels per carrier is small, which may lead to significant additional blocking.

With re-use factor 1, it appears is necessary to use a larger number of slots (eg 8) per channel to achieve sufficient coverage. Smaller slot allocations are sufficient for re-use factor 3.

12.3.2 Deployment Results - Vehicular Environment

In UMTS 30.03 the vehicular environment specifies sectored cells. The results here are presented for omni-directional antennas. The capacity figures per cell (i.e. per sector) should be similar for sectored cells. The standard deviation of shadowing was 10dB, with a propagation exponent assumed to be 4.

12.3.2.1 Speech

Here we consider as examples two possible schemes;

A:Single frequency re-use with link adaptation options of 1, 2, 4 and 6 slots per channel

B:Cluster size of 3 with 1/4, 1/2. 1 and 2 slot option.

For scheme A the C/I the offset for power control and fractional loading is 5dB. For scheme B only a 3dB offset for power control is applied. In scheme B the 1/2 and 1/4 slot options require the use of a multiplexed burst.

Table 10: Modulation/coding schemes (Speech, Vehicular A)

For comparison we also consider Scheme A in the Vehicular B channel.

Table 11: Modulation/coding schemes (Speech, Vehicular B)

Table 12 Spectral Efficiency (Speech, Vehicular A)

If can be seen that with Scheme A in re-use factor 1 the spectral efficiency is reduced by about 13% in the Vehicular B environment. This reduction might be larger with Scheme B, since shorter slot allocations would typically be used.

12.3.2.2 LCD384

In this case we consider 16 slots in a frame, and a 384kbps circuit switched bearer with a 3 frequency re-use pattern.

Table 13: Modulation/coding schemes (LCD 384, Vehicular A)

12.3.3.2 LCD384

Table 16: Modulation/coding schemes (LCD 384, Indoor A)

A 16 slot mode is needed to ensure coverage with re-use factor 3. The average number of slots per channel is 3.5, giving 12 channels per carrier. The Spectrum Efficiency is 5.8 Erlangs/Cell or 155kbps/MHz/Cell, with an average fractional loading of 49%. Clearly the small number of available channels limits the trunking efficiency.

12.4 Summary of Results

The results shown above were obtained using the analytical method outlined earlier. The main simplifying assumptions are that the users are stationary, the system is noise limited, and that omnidirectional antennas are deployed in hexagonal cells. This means that the modelling of the Pedestrian environment is compatible with the requirements of UMTS 30.03. The results in the other environments should be considered as indicative only.

Annex D:

Concept Group Delta δ - Wideband TDMA/CDMA

This report contained in this annex was prepared during the evaluation work of SMG2 as a possible basis for the UTRA standard. It is published on the understanding that the full details of the contents have not necessarily been reviewed by, or agreed by, ETSI SMG or SMG2.

Madrid, Spain

December 15-19, 1997

Source: SMG2

Concept Group Delta WB-TDMA/CDMA:

System Description Summary

Introduction

In the procedure to define the UMTS Terrestrial Radio Access (UTRA), the WBTDMA/CDMA concept group developed and evaluated a multiple access concept based on frequency, time, and code division.

The WB-TDMA/CDMA design rational is as follows:

∙CDMA component: To offer interferer diversity, to provide fine granularity of user data rates without high peak to mean powers.

∙TDMA component based on GSM timing structure: To build UTRA directly on top of proven GSM technology, to ensure easy handover between GSM and UMTS, to reduce the number of codes to be processed at the same time and hence make multi-user detection feasible from day 1 of UMTS. To take advantage of orthogonal partitioning of radio resources to avoid instability.

∙Benefit from near-far resistant multi user-detection (MUD): Cancellation of intra cell interference, to achieve stability without fast and accurate power control. To avoid soft handover.

∙Wideband carrier: To support high user bit rates required in UMTS, and to take advantage of frequency diversity.

Key technical characteristics of the basic system

Table 1 - WB-TDMA/CDMA key technical characteristics

Performance enhancing features (according to network operator choice)

∙BTS antenna hopping,

∙frequency hopping,

∙directive and/or adaptive antennas,

∙time slot hopping,

∙cell synchronization,

∙interference based DCA,

∙faster power control (for slow moving mobiles),

∙quality based power control,

∙co-channel multi-user detection (synchronized cells),

∙relaying and advanced relay protocols such as ODMA.

As in GSM: In order to ensure that frequency hopping can be utilized in an operating system at any time, the frequency hopping capability shall be mandatory in all mobile terminals.

In addition, future enhancements of UTRA could include performance improving features which could take advantage of software configurable mobile station concepts, e.g. Turbo codes and improved link adaptation.

WB-TDMA/CDMA Support for Relaying and ODMA: A feasibility study conducted by the Delta and Epsilon concept groups concluded that WB-TDMA/CDMA can support relaying and the ODMA protocol with negligible increase in mobile complexity or cost. The ODMA protocol breaks difficult radio paths into a sequence of shorter hops which enables lower transmit powers or higher data rates to be used. It is the goal of the protocol to choose the least cost route through the relaying system when the relays are moving and the radio paths are dynamically changing. Simulations have shown that relaying has the potential to improve coverage and flexibility and may also increase capacity by lowering transmission powers and associated intercell interference. Further details are provided in part 6 of the WB-TDMA/CDMA Evaluation Report.

System description

Figure 1 depicts the multiple access of WB-TDMA/CDMA. For comparison reasons the multiple access of GSM is depicted in Figure 1, too. In WB-TDMA/CDMA up to 8 traffic channels (TCH) are supported in a time slot and a frequency band of width 1.6 MHz. However, the number of 8 traffic channels (CDMA codes) is not sharp. It is also feasible to assign 9 or even more CDMA codes within a time slot. The traffic channels are separated at the receiver based on TCH specific CDMA codes. As can be seen from Figure 1 in both WB-TDMA/CDMA and GSM a TDMA frame consists of 8 time slots. The duration of the TDMA frame as well as time slots is exactly the same for both GSM and WB-TDMA/CDMA. This identical frame and time slot structure allows to build WB-TDMA/CDMA easily on top of proven GSM technology and ensures an easy handover between GSM and UMTS.