Gunnar Bark

Uplink admission control in WCDMA based on relative load estimates

When operating a cellular radio system at nearly full capacity, admitting yet another user may jeopardize the stability of the system as well as the performance of the individual users. Therefore, proper admission control is crucial. Prior art includes algorithms which limit the number of users or the uplink interference per cell. Both are known to yield roughly the same performance, but the former is difficult to configure, and the latter is based on a quantity which is hard to measure accurately. The core idea in this work is to predict the relative load of the system directly, given that a user is admitted. Then, the user will be admitted if the predicted load in the specific cell, and in its neighbors, is below some threshold. The proposed uplink relative load estimate is focused on WCDMA. It utilizes measurements readily available in that system, either periodically scheduled or from handover events. Multi-services are naturally handled, and availability of high data-rate services are automatically limited with respect to coverage, compared to services of lower data-rate. Simulations indicate that the admission control operates satisfactorily in different traffic situations with a universal parameter setting. Furthermore, the reporting overhead with periodical measurements can be avoided, since handover event-driven measurements yield roughly the same performance.

Performance of downlink shared channels in WCDMA radio networks

In order to avoid downlink channelization code shortage, a downlink shared channel (DSCH) has been specified for WCDMA systems. On DSCH, many packet data users with bursty traffic can share a single channelization code. However, since DSCH is transmitted from only one access point it provides no macro-diversity gain, as the dedicated channels (DCH) do via soft handover. A scheme that combines high rate DSCH and medium rate DCH is proposed. Basically, users close to the base stations are allocated DSCH in order to save channelization codes, whereas users close to the cell borders are allocated DCH to conserve base station transmission power. The scheme is compared with other packet data channel allocation schemes. The simulation results show that DSCH provides high packet data bit rates due to less channelization code blocking. This is however at the cost of high transmission power, due to lack of soft handover gain. The proposed scheme achieves equally good packet data bit rate as the pure DSCH scheme, but with considerably less base station transmission power.

Uplink transmission timing in WCDMA

In wireless network uplink communications, there is a tradeoff between transmission coordination to avoid overload situations, and distributed transmission decisions to adapt to fast channel variations. Here, uplink transmission timing (UTT) is proposed as a scheme to allow some load control support, while transmitting mainly when the channel is favorable. It utilizes channel state feedback in the form of power control commands, which already are available in the system. Simulations illustrate the transmission timing behavior, and also indicate that UTT is a power and inter-cell interference efficient scheme to transport data compared to traditional dedicated channels with continuous transmissions and to schemes where transmission decisions are random.