3G WCDMA Systems Research Articles

Enhancing the high speed downlink packet access operation of 3G WCDMA systems

ABSTRACTIn high‐speed downlink packet access (HSDPA), the combination of adaptive modulation and coding, hybrid automatic repeat request, and an extended multicode operation has replaced two fundamental aspects of wideband code division multiple access systems, namely, variable spreading factor and fast power control. Despite its enhanced characteristics, the HSDPA operation can be problematic when the majority of incoming traffic load consists of low data rate delay‐sensitive services such as mobile voice‐over‐Internet Protocol. To tackle this case, we propose an enhanced HSDPA operation that exploits multiple layers of the channelization code tree through a specifically designed packet scheduling and code allocation process. Enhanced HSDPA, when compared with the conventional HSDPA, provides a more flexible sharing of the available capacity and is able to increase the number of users that can be served with the required quality of service in terms of packet delay. The efficiency of the proposed scheme is confirmed by simulation results. Copyright © 2011 John Wiley & Sons, Ltd.

A Scheduling Algorithm with Dynamic Priority Assignment for WCDMA Systems

In third generation WCDMA systems, shared channels allow many users to jointly utilize a single orthogonal variable spreading factor (OVSF) code. In this paper, we propose a scheduling algorithm with dynamic priority assignment (DPA) which is designed for the downlink-shared channel (DSCH) of 3G WCDMA systems and operates within a cross layer framework. The DPA scheduler has low computational complexity and is able to provide QoS differentiation among traffic flows based on their delay sensitivity. Through the cross layer framework, DPA takes into account the variations of the wireless channel, and exploits processing gain to improve transmission quality and enable service provisioning when possible. Additionally, by providing a guaranteed rate per traffic flow at each scheduling period, DPA can offer a deterministic delay bound to each connection when transmissions are reliable. Stochastic delay guarantees under transmission power limitations are also provided when the traffic flows are identical. Simulation results show that DPA outperforms feasible earliest due date (FEDD), a variation of EDD for wireless environments.

Minimizing the Call Setup Delay Caused by Reconfigurations of Dedicated Channels at the Downlink of WCDMA

Reconfigurations of downlink dedicated channels are often necessary during call setup to eliminate code blocking encountered in 3G WCDMA systems. These reconfigurations increase not only the signaling overhead, but also the setup delay of the incoming call and may yield prohibitive delays if performed inefficiently. In this paper, we introduce a reconfiguration scheme which manages to minimize this additional setup delay with a tolerable increase in signaling overhead.

Markov Decision Process Based Multiple Codes Assignment in UMTS WCDMA Mobile Networks

For achieving high transmission rate in mobile multimedia communications, 3G WCDMA systems adopt the Orthogonal Variable Spreading Factor (OVSF) code tree to assign a single channelization code for each accepted connection. Based on the orthogonal characteristic of an OVSF code tree, an allocated code blocks the channelization codes that are on the descendant branches and the ancestral codes of the allocated code. Several researches have been proposed to overcome the code-blocking problem for maximizing system utilization. By using both the code assignment and reassignment mechanisms, the system utilization and code blocking can be improved. Nevertheless, the data rate of traffic classes in such single code assignment system should be powers of two of the basic rate, which is impractical and wastes the system capacity when the required rate is not powers of two of the basic rate. A good solution is to assign multiple codes to a new connection, but causes two drawbacks: high complexity of handling multiple codes and high cost from using more number of rake combiners. Consequently, there is a trade-off between waste rate and complexity of handling multiple codes assignments. In previous researches, high computation complexity of assigning multiple codes for a connection and large number of reassignment codes suppressed the advantage of reducing waste rate. Therefore, we propose an adaptive efficient partition algorithm with the Markov Decision Process (MDP) analysis approach to reduce the large number of reassignment codes while improving waste rate. There are two main motivations in the proposed approach. First, we propose an adaptive efficient partition algorithm to determine multiple codes based on the current state of the OVSF code tree for the new incoming connection. Second, after determining the multiple codes, we adopt the MDP analysis to assign the least-cost code for each determined code. Numerical results demonstrate that the proposed MDP approach yields the least number of reassignments and the least number of codes per connection while reducing waste rate significantly, as compared to other approaches.

Management of channelization codes at the forward link of WCDMA

We examine the orthogonal variable spreading factor (OVSF) code tree management problem at the forward link of 3G WCDMA systems. Considering single code operation, we evaluate the performance of a code selection scheme called recursive fewer codes blocked scheme (RFCB). RFCB manages to mitigate code blocking and thus minimizes the fragmentation of the OVSF code tree capacity. Simulation results demonstrate the efficiency of the RFCB scheme compared to previously proposed schemes.

Radio characteristics evaluation tests of an experimental 3G WCDMA system in Taiwan suburban environments

An experimental study on the radio characteristics of a 3G WCDMA system in a Taiwan suburban environment was conducted. This paper presents the results of handover behaviors. The examinations and performance evaluation are based on the measured Eb /I 0, mobile system transmitting power, bit‐error‐rate and frame‐error‐rate statistic distributions with respect to the time variations, which corresponds to different measurement locations, under individual and independent but appropriate design of experiment procedures. The corresponding radio characteristics are analyzed and evaluated according to the measured data.

Space-time processing for smart antennas in advanced receivers for the user terminal in 3G WCDMA systems

An adaptive multi-target space-time down-link receiver for user terminals of WCDMA systems under soft handoff is presented. The receiver consists of M antennas and K array processors, each one followed by a chip-rate equalizer and a despreader. The resulting K signals are combined in an "adaptive ratio combiner" which is updated by pilot common channel information in UTRA-FDD systems. All the structure in the FDD WCDMA downlink signal is exploited for improved performance. Simulation results for a stationary channel and for COST-259 channel models, for vehicle speed of 50 km/h, are presented.

Soft capacity modeling for WCDMA radio resource management

This work addresses wireless capacity models and capacity consumption models for 3G WCDMA system analysis. Uplink and downlink capacities are viewed as multiple heterogeneous circuit-switched and packet-switched pools of various bit rate channels, wherein traffic channels and control channels contend for the same capacity within a cell. An individual user's consumption of capacity is formulated as a function of the user's traffic class, activity factor and negotiated QoS. Simulation based analysis, of resource management algorithms that employ admission control and channel rate- and type-switching, are undertaken to compare results obtained using the proposed capacity and capacity consumption models to that obtained using existing homogeneous models. The primary results demonstrate that differentiating between channel modes, giving consideration to control channel utilization, and giving consideration to user's service type can each significantly impact the results and conclusions drawn from resource management protocol analysis.

Design and implementation of a turbo decoder for 3G W-CDMA systems

This paper presents the design and hardware implementation of a log-MAP turbo decoder used in the third generation (3G) mobile communication W-CDMA systems. The decoding algorithm is highly data dominated and needs many memories for data storing. The memory requirements are systematically investigated and optimized from two aspects: (1) an alternative called state metric difference-storing method is proposed to save the forward state metric (/spl alpha/) and the backward state metric (/spl beta/) memory up to 1/3; (2) the interleaver address memory is reduced by repeating the address calculation at each iteration. The experimental results on an FPGA prototype of the decoder show that it supports 2Mbits/s data rate with five iterations, and for code blocks of more than 2000, a bit error rate (BER) of 10/sup -6/-10/sup -7/ is achieved at E/sub b//N/sub o/=1.0 dB after only five iterations.

Dynamic bandwidth allocation with fair scheduling for WCDMA systems

Dynamic bandwidth allocation (DBA) will play an important role in future broadband wireless networks, including the 3G and 4G WCDMA systems. A code-division generalized processor sharing (CDGPS) fair scheduling DBA scheme is proposed for WCDMA systems. The scheme exploits the capability of the WCDMA physical layer, reduces the computational complexity in the link layer, and allows channel rates to be dynamically and fairly scheduled in response to the variation of traffic rates. Deterministic delay bounds for heterogeneous packet traffic are derived. Simulation results show that the proposed CDGPS scheme is effective in supporting differentiated QoS, while achieving efficient utilization of radio resources.