As a transport layer protocol, TCP is widely used in the various applications especially for video transmission in the mobile network. The TCP protocol not only provides an end-to-end connection to guarantee the reliability and in-order delivery of packets, but also shapes the transmission rate from the server to client through the mobile network. In wireless link, the available bandwidth varies significantly due to the changes in the underlying radio channel conditions. Traditional TCP congestion control has difficulties in adapting to these rapidly varying conditions which leads to low throughput and long delay. This paper analyzes the TCP issues in the mobile wireless network, and proposes two radio-aware TCP optimization solutions. The loose coupled radio-aware TCP optimization solution controls the parameters of TCP layer according to the cross-layer information which includes the client predicted rate and low layer's assisted information, while the close coupled radio- aware TCP solution modifies the traditional TCP congestion control mechanism to a novel TCP request- grant mechanism. The simulation proves the solutions can acquire significant TCP performance gain with extreme low latency.

Closed loop beamforming transmit diversity is a promising technique to improve the uplink transmission performance in cellular networks. This technique was recently incorporated into the 3GPP HSPA standard. This paper reflects on several design aspects of closed loop beamforming transmit diversity, including: precoded pilot channels design, precoding information determination when UE is in soft handover, and enhanced symmetric beamforming implementation.

There is substantial and growing motivation to deploy wireless relays in 3G+ and 4G networks both in residential and commercial contexts to achieve significant coverage extension and capacity increases at potentially relatively low cost. However, relays operating in shared spectrum may introduce interference thus potentially counterbalancing gains, and conversely, relays requiring a dedicated resource (for access or backhaul) may raise issues of efficiency and load balancing including under or over use of either relay or macro (base station) resources. In this paper, we consider these issues and propose new power control and mobility algorithms to overcome these challenges. Results of our detailed system simulations are presented demonstrating how substantial gains in user experience, capacity, and coverage extension may be obtained in the context of HSPA+.

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.

Multiple Input Multiple Output (MIMO) transmission improves downlink spectral efficiency and is a key feature of Release 7 High Speed Downlink Packet Access (HSDPA). When the Node-B is configured in the MIMO mode with secondary common control pilot channel (S-CPICH), the power amplifiers (PAs) for the two transmit antennas are not balanced. A common pre-coder is required to balance the PAs for legacy and dual-stream MIMO transmissions. In addition, codebook restriction is needed to balance the PAs for single-stream MIMO transmissions. Despite codebook restriction, MIMO performance degradation is small. Legacy user performance in a MIMO cell suffers due to power and interference penalties associated with the Secondary Common Pilot Channel (S-CPICH). By reducing the S-CPICH transmit power, this degradation can be reduced, without significantly compromising the channel estimation quality for MIMO users in the cell.

Higher Order Modulation (HOM, 64-QAM) and Multiple Input Multiple Output (MIMO) transmissions are two key features introduced in the Release 7 (HSPA+) WCDMA systems to improve downlink performance. This paper focuses on the performance analysis of 64-QAM and MIMO in the WCDMA system. We describe the equalizer design for supporting these features as well as the simulation results demonstrating the higher system throughput and better user experience provided by these features.

Circuit-Switched (CS) Voice Services over HSPA (CSoHS) was recently introduced for 3GPP WCDMA Release 7/8 systems. The benefits of this feature include improving voice and data system capacity by utilizing the enhancements offered by the shared packet transport of HSPA air interface while preserving the already widely deployed core networks. In this paper, we discuss the operation and implementation of CSoHS and analyze its performance via simulations. We show that the system capacity of CSoHS is significantly higher than Release 99 CS voice under similar system conditions and voice quality.

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.

In this paper, families of rate-compatible protograph-based LDPC codes that are suitable for incrementalredundancy hybrid ARQ applications are constructed. A systematic technique to construct low-rate base codes from a higher rate code is presented. The base codes are designed to be robust against erasures while having a good performance on error channels. A progressive node puncturing algorithm is devised to construct a family of higher rate codes from the base code. The performance of this puncturing algorithm is compared to other puncturing schemes. Using the techniques in this paper, one can construct a rate-compatible family of codes with rates ranging from 0.1 to 0.9 that are within 1 dB from the channel capacity and have good error floors.

In this paper, we study the potential benefit of base-station (BS) cooperation for downlink transmission in a modified Wyner-type multicell model. Besides the dirty-paper-coding (DPC) precoder, we also analyze several linear precoding schemes, including co-phasing, zero-forcing (ZF) and MMSE precoders. For the nonfading case, analytical sum rate expression is obtained for each scheme. In networks of a large number N of cells, a high signal-to-noise-ratio (SNR) asymptotic gap is shown between the sum rate performances of DPC and ZF precoders. Moreover, the MMSE precoder sum rate expression in large networks indicates different behaviors of MMSE precoder in different SNR regimes: in the SNR > N2regime, it coincides with the ZF precoder, while, in the SNR2regime, it coincides with the co-phasing precoder. For the Rayleigh fading case, Monte-Carlo simulations demonstrate the effectiveness of linear precoding schemes with the proposed user selection criterion.

A general framework is provided to characterize the link level performance of CDMA systems with interference cancellation. This closed-form residual power analysis accounts for the impact of channel estimation errors due to SNR, channel variation, chip asynchronism, and filter mismatch. Simulations further quantify the link level cancellation performance on more realistic sub-chip multipath channels. This work demonstrates that properly designed channel estimation and signal reconstruction techniques achieve high cancellation efficiency over a variety of multipath fading channels.

This paper addresses the network level aspects of incorporating interference cancellation into the CDMA2000 1xEV-DO Revision A reverse link. We illustrate how a physical layer analysis of interference cancellation can be applied to an extensive network simulation environment that models inter-cell interference, hybrid-ARQ, multipath fading channels and the MAC-layer dynamics of power control, rate allocation, and rise- over-thermal control. An investigation of reverse link pilot channel performance and rise-over-thermal distribution shows that interference cancellation can be added to the base station processing without modifying the overall network operation or system stability. Network simulation results demonstrate how interference cancellation increases the data rate of each user to significantly improve the throughput achieved with both 2 and 4 receiver antennas per sector.

In this paper, we design families of rate-compatible structured LDPC codes suitable for hybrid ARQ applications with high throughput. We devise a systematic technique of low complexity for the design of structured low-rate LDPC codes from higher rate ones. These codes have a good performance on the AWGN channel and are robust against erasures and puncturing. The codes designed here are protograph-based codes and have fast encoding and decoding structures. These low rate codes are used as the parent codes of rate-compatible families. Then, we propose a number of algorithms for puncturing the codes in a rate compatible manner to construct codes of higher rates. The two most promising ones are the random puncturing search technique and progressive node puncturing. We show that using the techniques in this paper one could construct a high throughput rate compatible family with codes whose rates are in the range from 0.1 to 0.9 and which are within 1 dB from the channel capacity and have good error floors

We design serial concatenated multi-input multi-output systems based on low-density parity-check (LDPC) codes. We employ a receiver structure combining the demapper/detector and the decoder in an iterative fashion. We consider the a posteriori probability (APP) demapper, as well as a suboptimal demapper incorporating interference cancellation with linear filtering. Extrinsic information transfer (EXIT) chart analysis is applied to study the convergence behavior of the proposed schemes. We show that EXIT charts match very well with the simulated decoding trajectories, and they help explain the impact of different mappings and different demappers. It is observed that if the APP demapper transfer characteristics are almost flat, the LDPC codes optimized for binary-input channels are good enough to achieve performance close to the channel capacity. We also present a simple code-optimization method based on EXIT chart analysis, and we design a rate-1/2 LDPC code that achieves very low bit-error rates within 0.15 dB of the capacity of a two-input two-output Rayleigh fading channel with 4-pulse amplitude modulation. We next propose to use a space-time block code as an inner code of our serial concatenated coding scheme. By means of a simple example scheme, using an Alamouti inner code, we demonstrate that the design/optimization of the outer code (e.g., LDPC code) is greatly simplified.

For some channels, channel side information at the transmitter (CSIT) may not improve channel capacity. For example, for binary input and symmetric output memoryless channels, uniform input distribution is capacity achieving with or without CSIT. However, we show that CSIT can help reduce the complexity of codes if the code is designed using channel knowledge and provide for lower bounds on complexity. A code optimization problem for minimizing complexity for a given rate loss is also posed.

We design multilevel coding (MLC) and bit-interleaved coded modulation (BICM) schemes based on low-density parity-check (LDPC) codes. The analysis and optimization of the LDPC component codes for the MLC and BICM schemes are complicated because, in general, the equivalent binary-input component channels are not necessarily symmetric. To overcome this obstacle, we deploy two different approaches: one based on independent and identically distributed (i.i.d.) channel adapters and the other based on coset codes. By incorporating i.i.d. channel adapters, we can force the symmetry of each binary-input component channel. By considering coset codes, we extend the concentration theorem based on previous work by Richardson et al. ( see ibid., vol.47, p.599-618, Feb. 2001) and Kavc/spl caron/ic/spl acute/ et al.(see ibid., vol.49, p.1636-52, July 2003) We also discuss the relation between the systems based on the two approaches and show that they indeed have the same expected decoder behavior. Next, we jointly optimize the code rates and degree distribution pairs of the LDPC component codes for the MLC scheme. The optimized irregular LDPC codes at each level of MLC with multistage decoding (MSD) are able to perform well at signal-to-noise ratios (SNR) very close to the capacity of the additive white Gaussian noise (AWGN) channel. We also show that the optimized BICM scheme can approach the parallel independent decoding (PID) capacity as closely as does the MLC/PID scheme. Simulations with very large codeword length verify the accuracy of the analytical results. Finally, we compare the simulated performance of these coded modulation schemes at finite codeword lengths, and consider the results from the perspective of a random coding exponent analysis.

We design multilevel coding (MLC) schemes with low-density parity-check (LDPC) codes as component codes at each level. We develop a method to analyze the performance of an LDPC code at any level as the codeword length goes to infinity, even if the equivalent binary-input component channels are not symmetric. By joint optimization of code rates and degree distributions, the optimized irregular LDPC codes at each level are capable of achieving reliable transmission at signal-to-noise ratios (SNR) very close to the capacity of the additive white Gaussian noise (AWGN) channel as the codeword length tends to infinity. Simulation results show that the optimized LDPC codes also perform very well at moderate codeword lengths.

We design low-density parity-check (LDPC) codes for bandwidth efficient modulation using a multilevel coding (MLC) technique. We develop a method to analyze the asymptotic performance of the LDPC codes using message-passing decoding at each level of the MLC scheme as the codeword length goes to infinity. Simulation of very large block size LDPC codes verifies the accuracy of the analytical results. We jointly optimize the code rates and code parameters of the LDPC codes at each level of the MLC scheme, and the asymptotic performance of the optimized irregular LDPC codes is very close to the channel capacity of the additive white Gaussian noise (AWGN) channel.

A numerical method has been presented to determine the noise thresholds of low density parity-check (LDPC) codes that employ the message passing decoding algorithm on the additive white Gaussian noise (AWGN) channel. In this paper, we apply the technique to the uncorrelated flat Rayleigh fading channel. Using a nonlinear code optimization technique, we optimize irregular LDPC codes for such a channel. The thresholds of the optimized irregular LDPC codes are very close to the Shannon limit for this channel. For example, at rate one-half, the optimized irregular LDPC code has a threshold only 0.07 dB away from the capacity of the channel. Furthermore, we compare simulated performance of the optimized irregular LDPC codes and turbo codes on a land mobile channel, and the results indicate that at a block size of 3072, irregular LDPC codes can outperform turbo codes over a wide range of mobile speeds.