Nagabhushana T. Sindhushayana

Optimal resource allocation for data service in CDMA reverse link

The optimal resource allocation policy is studied in this paper, for nonreal-time users in CDMA reverse link. The resource allocation policy of interest includes channel coding, spreading gain control and power allocation under the conventional receiver operation-multiuser detection technique is not considered. The constraints in the optimization include peak transmit power of the mobile station, total received power at the base station and QoS in the form of minimum SINR for each user. The coding and spreading gain control can be separated from the power allocation strategy. Our results show that the optimal power allocation policy depends on the objective function: to maximize the sum of throughput from each user, a greedy policy is optimal where the good users (mobile stations with good radio conditions) transmit with full power, bad users (mobile stations with poor radio conditions) barely achieve their QoS and there is at most one user in-between; on the other hand, to maximize the product of throughput from each user, a fair policy is optimal where the bad users transmit with full power and the good users transmit with powers to reach a common received power level. The fairness of the optimal policy in the latter case makes QoS constraint unnecessary. Furthermore, we have found a unified approach in deriving these optimal policies. This approach can also be applied to other power allocation problems in CDMA reverse link. We also present numerical results on the channel capacity under both objectives and the effect of QoS constraint.

Heterogeneity and multi-cell cooperation in wireless cellular networks

The performance of most urban cellular networks is limited by inter-cell interference. This is particularly true of a cellular network with heterogeneous infrastructure, wherein the same spectrum is shared by different types of base-stations such as macro-cells, pico-cells, femto-cells and relays. Performance of such dense/heterogeneous deployments may be greatly enhanced through the use of smart association techniques, coupled with adaptive interference management. Unlike traditional cellular systems where association is predominantly based on maximizing signal quality between the base-station and the user, a smart association scheme in a heterogeneous network should be based on several additional criteria such as aggressive load-balancing, path-loss minimization, or minimization of interference to other links. Aggressive load-balancing (in particular) requires advanced interference management, which can may be realized through (soft) resource partitioning, beam-coordination or joint signal processing at the base-stations. Multi-cell signal processing (or distributed MIMO) can be used in homogeneous networks as well, in order to mitigate inter-cell interference without compromising degrees of freedom associated with the transmit signals. In this tutorial, we demonstrate how these techniques may be incorporated into the design of a cellular system, and the performance gains resulting from such a system design.