Danlu Zhang

Optimal resource allocation in multiservice CDMA networks

This paper addresses the problem of dynamic resource allocation in a multiservice direct-sequence code-division multiple-access (DS-CDMA) wireless network supporting real-time (RT) and nonreal-time (NRT) communication services. For RT users, a simple transmission power allocation strategy is assumed that maximizes the amount of capacity available to NRT users without violating quality of service requirements of RT users. For NRT users, a joint transmission power and spreading gain (transmission rate) allocation strategy, obtained via the solution of a constrained optimization problem, is provided. The solution maximizes the aggregate NRT throughput, subject to peak transmission power constraints and the capacity constraint imposed by RT users. The optimization problem is solved in a closed form, and the resulting resource allocation strategy is simple to implement as a hybrid CDMA/time-division multiple-access strategy. Numerical results are presented showing that the optimal resource allocation strategy can offer substantial performance gains over other conventional resource allocation strategies for DS-CDMA networks.

Optimal Resource Allocation for Data Service in CDMA Reverse Link

The optimal resource allocation policy is studied for non-real-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. 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: a greedy policy is optimal to maximize the sum of throughput from each user, whereas a fair policy is optimal to maximize the product of throughput from each user. A unified approach is taken to derive the optimal policies, and it can also be applied to other power allocation problems in CDMA reverse link. Numerical results of the channel capacity are presented for both objectives along with the effect of QoS constraints.

Concurrent bandwidth aggregation over wireless networks

Mobile client platforms have emerged with the ability to access and utilize multiple wireless networks concurrently. Aggregation can be performed using wireless modems on one device or cooperatively across devices within wireless proximity of each other. This paper explores various concurrent bandwidth aggregation schemes. The aggregation can be achieved on the application-layer, transport layer like MultipathTCP, or on layers below IP such as the RLC layer. These schemes are compared. In general, aggregation on the lower layer is closer to the client device and easier to adapt to the varying channel and loading conditions. However, lower layer aggregation needs more changes to wireless access stratum infrastructure. Aggregation above the IP layer is simpler to implement. A feasibility study of MultipathTCP aggregation over multiple WWANs is presented.

Performance Analysis of Dual-Carrier HSDPA

The newly standardized Dual-Carrier HSDPA offers two-carrier aggregation on the downlink. In this paper, we investigate the performance gains from the dual-carrier operations with both full buffer and bursty traffic models. With full buffer traffic, dual-carrier offers dynamic load balancing and increase in user data rate, system capacity and spectral efficiency. All the users throughout the system enjoy the data rate increase. With bursty traffic, dual-carrier provides substantial gain in user experience measured by burst rates or latency under all loading conditions. Moreover, the gain with bursty traffic is universal not only for all the users but also for a very wide range of scheduling algorithms. Our results are based on analysis and extensive simulations. Design issues are also addressed in this paper.

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.

COBA: Concurrent Bandwidth Aggregation - A Case Study in Parallel Wireless Communications

Parallel Wireless Communications is an emerging area of research that enables mobile clients to access and utilize multiple wireless networks concurrently. This paper explores concurrent bandwidth aggregation techniques to enable parallel wireless communications on mobile devices. Concurrent aggregation can be performed using wireless modems on one device or cooperatively across devices within wireless proximity of each other.. The aggregation can be achieved on the application-layer, transport layer like MultipathTCP, or on layers below IP such as the RLC layer. These schemes are compared. In general, aggregation on the lower layer is closer to the client device and easier to adapt to the varying channel and loading conditions. However, lower layer aggregation needs more changes to wireless access stratum infrastructure. Aggregation above the IP layer is simpler to implement. A feasibility study of MultipathTCP aggregation over multiple WWANs is presented. The aggregation scheme on the RLC layer in evolved HSDPA is also presented, including protocol design and performance evaluation.

Performance Gains of Single-Frequency Dual-Cell HSDPA

In this paper, we will study the scheme of Single-Frequency Dual-Cell HSDPA (SF-DC HSDPA) which is introduced to simultaneously transmit two separate packet streams from two cells to a mobile. The inter-stream interference is suppressed by the linear-MMSE equalizer at the mobile. In the simple implementation studied in this paper, the schedulers at the two cells are independent without information exchange. Our study is based on both analysis and simulations. SF-DC HSDPA offers significantly higher data rates to users in the handover region. It also achieves dynamic load balancing in terms of resource utilizations across cells. Furthermore, all these gains can be obtained without degrading the performance of users not in handover and the legacy users. The gain from SF-DC is particularly substantial for users in heavily loaded cells surrounded by lightly loaded neighboring cells. In addition, such gain can increase with loading at a given loading ratio between the heavily loaded and lightly loaded cells. SF-DC is easy to implement with only incremental complexity to the current mobile and network equipment.

Admission control for cellular networks with direct QoS monitoring

This paper proposes an admission control algorithm for cellular networks based on the direct and dynamic monitoring of quality of services (QoS) performance metrics—both system delay tail and residual throughput. The main purpose of directly monitoring these QoS performance metrics is to more precisely meet the QoS requirements. The delay tail is efficiently estimated by the proposed algorithm and the total residual throughput is determined based on the total achieved throughput and total required throughput. With the estimated delay tails and measured residual throughput, the admission or rejection of a new user is determined at each base station. By doing so, the admission control algorithm improves resource utilization by guaranteeing the QoS. Additionally, the cellular system becomes more robust against the time-varying fading channel environment. The simulation results of the long term evolution downlink system show that the proposed algorithm can achieve a significant improvement in results compared to those of reference schemes. A general Neyman–Pearson-like framework is also used in evaluating the various admission control mechanisms.

System performance of Inter-NodeB MF-HSDPA with RLC and MAC enhancements

In this paper, we study the feature of Multi-Flow HSDPA (MF-HSDPA), which allows simultaneous transmission of separate data packets from two or more serving cells (across different sectors or NodeBs) to a UE. This new feature brings challenges for system design, especially for the Inter-NodeB case, in which the serving cells reside in different NodeBs. To address these challenges, we propose enhancements to the Radio Link Control (RLC) layer and Media Access Control (MAC) layer. Simulation results show significant performance gain can be achieved by the MF-HSDPA feature.

QoS Performance Based Admission Control in Cellular Networks

In this paper. we consider an admission control algorithm for cellular networks. It is based on direct/dynamic monitoring of the QoS performances -- the delay tail of the admitted users. The main purpose of the direct monitoring of QoS performances is to guarantee the required QoS provision more precisely. The system delay tail is effectively computed by the proposed delay tail estimation algorithm. With the estimated delay tails, each base station determines the admission or rejection for a new user to the system. By doing so, the admission control algorithm becomes more robust against time-varying fading channel environment. Simulation results in OFDMA cellular system shows that the proposed algorithm can provide substantial capacity gains in offering QoS. We also use a general Neyman-Pearson-like framework in evaluating various admission control mechanisms.