Литература / UMTS-Report

Figure 30 Eb/No vs BL.E.R. ( Mode A, Office)

Figure 31 Eb/No vs BL.E.R. ( Mode A, Pedestrian)

Figure 32 Eb/No vs BL.E.R. ( Mode A, Vehicular)

10.4.2 Mode B

Table 10: Simulation parameters for UUD384 Mode B

Figure 33 Eb/No vs BL.E.R. ( Mode B, Office)

Figure 34 ( Mode B, Office)

10.5 UDD 2048 Simulation

10.5.1 Mode B

Table 11: Simulation parameters for UUD2048 Mode B

Figure 37 Eb/No vs BL.E.R. (UUD2048, Pedestrian)

11. Link Level Results (Coherent Operation)

For the coherent operation mode the Indoor scenario was considered first.

Indoor link level simulations were performed for packets of 14400 bits (6 blocks of 4 symbols for coherent, 24 symbols for differential). No antenna diversity was used. Bit and packet error ratios were obtained by averaging over 1000 independent channels, according to the indoor model A. For the highest data rate, each OFDM symbol has 600 subcarriers, so the data rate is 2.08 Mbps. The total number of subcarriers is 3600 in a bandwidth of 15 MHz. QPSK with rate ½ coding was used (constraint length 7).

Figure 38 shows bit and packet error ratios versus Eb/No without power control. Figure 39 shows the same results with power control. In this case, the results are much better because Eb/No is now constant for each packet. For a BER of 10-3, for instance, about 5.5 dB Eb/No is required for coherent detection, which is about 10 dB better than the average required Eb/No in the case of no power control. However, it should be noted that this improvement holds for the mean Eb/No at the input of the receiver. Eb/No does not include any increase in the average transmit power, which will be present in the case of power control.

Figure 38: a) BER for coherent detection, b) BER for differential detection in the frequency domain, c) Packet Error Ratio (PER) for coherent detection, d) PER for differential detection.

Figure 39: BER and PER for perfect power control, a) BER for coherent detection, b) BER for differential detection, c) PER for coherent detection, d) PER for differential detection

The 5 Hz Doppler in the indoor channel model A has no effect at all, because the packets are too small to benefit from time diversity. Even for circuit switched data, the maximum interleaving time is too short to get a significant improvement. So, the BER plots apply to any rate, provided that a proper interleaving in frequency is done such that the system benefits from the full frequency diversity.

C/(I+N) for each slot is collected, and the raw BER is found. (The raw BER are calculated values for all slots within one interleaver frame.) The mean raw BER is then calculated, and finally, the coded BER is calculate by mean raw BER using another look up table. These look up tables are created by the link level simulation. The impact of the channel impulse response model is taken into account for each look up table for each specific evaluation environment. For diversity antenna reception, we collect the raw BER value for each branch, and calculate the mean raw BER.

In actual operation, a cross interleaver will be implemented to reduce transmission delays. However for the system level simulations a cross interleaver is not used to simplify simulations. This does not influence the performance. Interleaving is achieved over 18.46msec (speech service). Currently, only co-channel interference from other cells is taken account, and the interference caused by adjacent channel spurious emission is ignored.

For speech services, OFDMA uses a 4 TDMA structure with channel spacing of 100kHz. For a 15MHz system bandwidth the OFDMA system has 600 (15000kHz / 100kHz * 4 TDMA) logical channels. To reduce the simulation time only 1 time slot was simulated. The performance in the other slots was assumed to be the same. In addition, a system bandwidth of only 3.2 MHz was used in order to reduce the number of logical channels and shorten the simulation time. Evaluation with 3.2 MHz bandwidth (32 logical channel per cell) was regarded as reliable enough to measure the precise interference distribution/density.

32 logical channel per cell is however too small to achieve the required trunking efficiency. For a 90% system load which corresponds to 600 logical channel per cell, all of the system traffic can be accommodated without blocking. By evaluating the same load of the system which has only 32 logical channel per cell, the system will block about 8% of the users (see Figure 41). To compensate for this the blocked user rate is calculated by simulating the exact blocked user rate assuming 600 logical channel by using another look up table.

Figure 42 shows the results for satisfied users versus system load for 3.2 MHz and 32 channels and Figure 43 shows percentage of blocked users versus accommodated load for the same conditions. By using the look up table the results for 600 channels in 15 MHz are shown in Figure 44. It can therefore be seen that blocking does not occur at a load of 135kbps/MHz/cell. For a speech service with 15MHz system bandwidth, blocking can therefore be ignored. Additionally, at 32 channels per cell case, it is impossible to achieve a load of greater than 135 kbps/MHz/cell.