Qualcomm

Madhavan Vajapeyam, Student Member, IEEE, Jifeng Geng, and Urbashi Mitra, Fellow, IEEE

Space–time block codes (STBCs) have attracted recent interest due to their ability to take advantage of both space and time diversity to reliably transmit data over a wireless fading channel. In many cases, their design is based on asymptotically tight performance criteria, such as the worst-case pairwise error probability (PEP) or the union bound. However, these quantities fail to give an accurate performance picture, especially at low signal-to-noise ratio, because the classical union bound is known to be loose in this case. This paper develops tighter performance criteria for STBCs which yield considerably better bounds. First, the union bound is developed as the average of the exact PEPs. By noting that some of the terms in the bound are redundant, a second bound is obtained by expurgation. Since this still yields a loose bound, a tighter bound, denoted as the progressive union bound (PUB), is obtained. Because the PUB cannot be computed in closed form, in its most general case, and to avoid computing a high-dimensional numerical integration, its saddlepoint approximation is developed. In addition to the significant improvement of the PUB analysis over other bounding methods, it is also shown that codes designed to optimize the PUB can perform better than those obtained by the looser criteria.

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Copyright © 2007 IEEE. Reprinted from IEEE Communications Magazine.

Xiliang Luo, Member, IEEE, and Georgios B. Giannakis, Fellow, IEEE

Timing synchronization of symbol boundaries is known to affect critically the performance of all coherent communication systems. Its effects are particularly pronounced in contemporary wireless technologies including ultrawideband (UWB) radios and wireless sensor networks (WSNs), where cooperative or ad hoc access is challenged by arbitrary asynchronism, intersymbol interference (ISI), receiver noise, as well as inter and intrapiconet interference arising from concurrently communicating nodes. To cope with these challenges, this paper introduces piconet-specific synchronization patterns and simple averaging operations at the receiving ends, which enable low-complexity timing acquisition through energy detection and demodulation by matching to a synchronized aggregate template (SAT). Pattern sequences are designed for both training-based and blind operation. Either way, the idea behind these designs is to periodically increase the transmit-power (“voice”) of each piconet’s synchronizing node with a period (“pace”) characteristic of each piconet. Performance of the novel synchronization protocols is tested with simulations conforming to an UWB wireless personal area network (WPAN) setup.

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Copyright © 2007 IEEE. Reprinted from IEEE Communications Magazine.

Paul J. Draxler,Anding Zhu, Jonmei J. Yan, Pavel Kolinko, Donald F. Kimball, Peter M. Asbeck

This paper demonstrates a method to quantify the accuracy of memory models and the effectiveness of digital predistortion of power amplifiers with memory. By using assumptions of periodic stationarity, coherent ensemble averaging and a stable measurement system, we are able to decompose the waveform distortion into memoryless, deterministic memory, and random memory contributions. We demonstrate how this can be used to evaluate the performance of a power amplifier and project its optimal performance with predistortion. We also show experim~ntall~ ~hat the ~yna~c deviation reduction-based Volterra serIes dIgItal predlstortIon technique has convergent behavior, moving towards t~ese quantified targets when applied to a class AB power amplIfier implemented with GaN FETs.

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Copyright © 2008 IEEE. Reprinted from IEEE Communications Magazine.

Radhika Gowaikar, Student Member, IEEE, Amir F. Dana, Student Member, IEEE, Babak Hassibi, and Michelle Effros, Senior Member, IEEE

In many problems in wireline networks, it is known that achieving capacity on each link or subnetwork is optimal for the entire network operation. In this paper, we present examples of wireless networks in which decoding and achieving capacity on certain links or subnetworks gives us lower rates than other simple schemes, like forwarding. This implies that the separation of channel and network coding that holds for many classes of wireline networks does not, in general, hold for wireless networks. Next, we consider Gaussian and erasure wireless networks where nodes are permitted only two possible operations: nodes can either decode what they receive (and then re-encode and transmit the message) or simply forward it. We present a simple greedy algorithm that returns the optimal scheme from the exponential-sized set of possible schemes. This algorithm will go over each node at most once to determine its operation, and hence, is very efficient. We also present a decentralized algorithm whose performance can approach the optimum arbitrarily closely in an iterative fashion.

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Copyright © 2007 IEEE. Reprinted from IEEE Communications Magazine.

Jinghu Chen, Member, IEEE, R. Michael Tanner, Fellow, IEEE, Juntan Zhang, and Marc P. C. Fossorier, Fellow, IEEE

In this correspondence, we propose an approach to construct irregular low-density parity-check (LDPC) codes based on quasi-cyclic extension. When decoded iteratively, the constructed irregular LDPC codes exhibit a relatively low error floor in the high signal-to-noise ratio (SNR) region and are subject to relatively few undetected errors. The LDPC codes constructed based on the proposed scheme remain efficiently encodable.

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Copyright © 2007 IEEE. Reprinted from IEEE Communications Magazine.

Chien-Chung Shen and Ke Li, Chaiporn Jaikaeo, Vinay Sridhara

The minimum-energy multicast tree problem aims to construct a multicast tree rooted at the source node and spanning all the destination nodes such that the sum of transmission power at non-leaf nodes is minimized. However, aggressive power assignment at non-leaf nodes, although conserving more energy, results in multicast trees that suffer from higher hop count and jeopardizes delaysensitive applications, signifying a clear tradeoff between energy efficiency and delay. This article formulates these issues as a constrained Steiner tree problem, and describes a distributed constrained Steiner tree algorithm, which jointly conserves energy and bounds delay for multicast routing in ad hoc networks. In particular, the proposed algorithm concurrently constructs a constrained Steiner tree, performs transmission power assignment at non-leaf nodes, and strives to minimize the sum of transmission power of non-leaf nodes, subject to the given maximum hop count constraint. Simulation results validate the effectiveness and reveal the characteristics of the proposed algorithm.

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Copyright © 2005 IEEE. Reprinted from IEEE Communications Magazine.

Xiliang Luo and Georgios B. Giannakis

As low power, low cost and longevity of transceivers are major requirements in wireless sensor networks, optimizing their design under energy constraints is of paramount importance. To this end, we develop quantizers under strict energy constraints to effect optimal reconstruction at the fusion center. Propagation, modulation, as well as transmitter and receiver structures are jointly accounted for using a binary symmetric channel model. We first optimize quantization for reconstructing a single sensor’s measurement. Optimal number of quantization levels and optimal energy allocation across bits are derived. We then consider multiple sensors collaborating to estimate a deterministic parameter in noise. Similarly, optimum energy allocation and optimum number of quantization bits are derived analytically and tested with simulated examples.

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Copyright © 2004 IEEE. Reprinted from IEEE Communications Magazine.

Ozcan Ozturk, Vinay Chande, Haitong Sun, Mehmet Yavuz, Bibhu Mohanty, Mario Scipione

We analyze the performance of voice services over 3GPP WCDMA Networks for Release 99 and Release 7 deployments. We show, by using simulations, that the system capacity of Release 7 VoIP is significantly higher than the Release 99 circuit-switched voice under similar system conditions and voice quality. These results are obtained under the 3GPP simulation assumptions where uplink and downlink constraints for power, code and interference are considered. Both AMR 12.2 and 5.9 as well as different types of mobile receivers (Rake and equalizer, single and dual receive antennas) are considered. We also show that the capacity and performance can be increased significantly further by using uplink interference cancellation at the base station. The performance of best effort traffic in the presence of voice users is also analyzed.

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Copyright © 2008 IEEE. Reprinted from IEEE Communications Magazine.

Danlu Zhang, Sharad Sambhwani and Bibhu Mohanty

This paper discusses several important aspects in the HSUPA scheduling algorithms. First, it clearly demonstrates the benefit of explicitly utilizing the directly measured Rise-over- Thermal(RoT) values in term of capacity and robustness improvement. This paper also briefly presents the RoT measurement schemes designed specifically for the asynchronous systems such as WCDMA /HSUPA. If pilot and traffic interference cancellation (IC) schemes are implemented at the Node B receiver, this paper presents a scheduling algorithm that attains IC benefit in such a way that the capacity enhancement is maximized while fairness and link budget are maintained. The presented algorithm defines the effective RoT by monitoring the IC performance in real time and adjusts its grants accordingly. In addition, the user priority function used here optimizes the sum utility functions and provides multi-user diversity.

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Copyright © 2008 IEEE. Reprinted from IEEE Communications Magazine.

Rohit Kapoor, Siddharth Mohan and Srini Eravelli

Legacy Serving Cell Change (pre-release 8 SCC) procedure produce unacceptably high call drop rates (as high as 10% in some scenarios) in realistic Urban Canyon conditions obtained from field logs when Signaling Radio Bearers (SRB) are mapped on the High Speed Downlink Shared Channel (HS-DSCH). Mapping SRB on HS-DSCH is necessary to enable high capacity voice over HSPA. Using simulations, the performance of Enhanced SCC procedure (ESCC) is shown to be very reliable under Urban Canyon conditions. In addition to simulations, the performance of legacy USCC and the ESCC procedures implemented in our prototype HSPA system is studied in the presence of other features recommended for VoIP such as Robust Header Compression (RoHC), De-jitter buffer at the UE, HS-PDSCH scheduler and bicasting. Results from prototype testing confirm simulation results, i.e., that under tough urban canyon conditions, the enhanced SCC procedure provides significant gains, in terms of packet drops and duration of serving cell change, compared to the legacy SCC procedure. We conclude that the enhanced SCC procedure standardized in HSPA Release 8 provides a very robust solution for handling of mobility over HSDPA , and provides good performance even under severe urban canyon-like scenarios.

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Ozcan Ozturk, Rohit Kapoor, Bibhu Mohanty and Mario Scipione

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

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Sharad Sambhwani, Wei Zhang, and Wei Zeng

This paper provides the principles and practice of how interference cancellation (IC) can be implemented for the uplink in a 3GPP HSPA NodeB (Base Station) receiver. Uplink interference cancellation is a capacity enhancing technique that can be added to a NodeB receiver without the need to modify user equipment (UE), 3GPP specifications or network coverage. Details are provided on the algorithm, implementation and the corresponding system performance.

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Sharad Sambhwani, Wei Zhang, and Wei Zeng

In the paper titled “Uplink Interference Cancellation in HSPA: Principles and Practice” an interference cancellation (IC) scheme for the uplink of WCDMA/HSPA was presented. The motivation, theory, practical algorithms and the associated system performance benefits were presented. In this paper, we focus on the complexity analysis of the proposed IC scheme. Traditional hardware and software design philosophy usually considers the factors that influence processing power as deterministic variables. The design is typically dimensioned for the worst case situation. However, user behaviors such as packet arrival and successful decoding at the NodeB (Base Station) receiver are all random processes that cannot be described deterministically. The techniques of discrete event simulation are well suited to investigate the system requirement in the early stage of design. In this paper, we describe a methodology using discrete event simulation to study the complexity of the proposed IC scheme.

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Jilei Hou, John E. Smee, Henry D. Pfister, Stefano Tomasin

This article provides the principles and practice of how interference cancellation can be implemented on the EV-DO Rev A reverse link. It is shown that applying interference cancellation to CDMA achieves the multiple access channel sum rate capacity for either frame synchronous or asynchronous users. The per user SINR gain from space-time interference cancellation translates directly into a CDMA capacity gain of the same factor, allowing EV-DO Rev A to support more users with higher data rates. We demonstrate how interference cancellation can be added to base station processing without modifying user terminals, EV-DO standards, or network coverage. We present commercially viable receiver architectures for implementing interference cancellation with the asynchronism and H-ARQ of EV-DO RevA, and explain why closed loop power control can operate the same way it does today. Network level simulations over a wide range of channels confirm that interference cancellation offers significant capacity gains for all users, while maintaining the same link budget and system stability.

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Copyright © 2007 IEEE. Reprinted from IEEE Communications Magazine.

Ahmed K. Sadek, Wenyi Zhang and Stephen J. Shellhammer

The spectrum sharing problem between heterogeneous networks that are not interoperable is considered. Two strategies for interference management are studied. First, by treating the possible interference from adjacent transmitters as noise, each transmitter can achieve a certain information rate which merely depends upon the channel quality, but does not depend upon the burstiness of packets arrival. Second, in an ideal listen-before-talk (LBT) strategy, where perfect sensing between transmitters is assumed, the stable achievable rates of the pairs of transceivers are analyzed, and shown to exhibit interaction and dependence upon the bursty arrivals of packets. It is revealed that, for receivers in certain regions which are exposed to strong interference and low traffic burstiness, LBT performs better; while in the other regions with decreased interference level or higher traffic loads, treating interference as noise leads to better performance.

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Copyright © 2008 IEEE. Reprinted from New Frontiers in Dynamic Spectrum Access Networks.

Murali R. Chari, Fuyun Ling, Ashok Mantravadi, Raghuraman Krishnamoorthi, Rajiv Vijayan, G. Kent Walker, and Rob Chandhok

This paper provides an overview of the physical layer of the Forward Link Only (FLO) Air Interface. The FLO Air Interface is a key component of the MediaFLO system developed by QUALCOMM as an alternative mobile multicast technology for the efficient transmission of multiple multi-media streams to mobile devices using TV and multi-media channel bandwidths in VHF, UHF, or L-band. The main concepts and features of the FLO Air Interface including the modulation and coding techniques used, the frame structure, and the different sub-channels within the physical layer are described. The available data rates as well as other characteristics of FLO are also described. Finally, the performance of the FLO physical layer in representative channel environments is presented.

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Copyright © 2007 IEEE. Reprinted from IEEE Transactions on Broadcasting.

Xin Zhang, Jun Chen, Stephen B. Wicker, Toby Berger

In this correspondence, we show that solutions to the multiple description coding problem and the broadcast channel coding problem share a common encoding procedure: successive source encoding. We use this connection as the basis for establishing connections between the achievable multiple description rate region and Marton’s region for broadcast channels. Specifically, we show that Marton’s encoding scheme can be viewed as a multiple description coding procedure.We also explore the dual problem, namely, the relationship between successive channel decoding in multiple access communication and distributed source coding. By illuminating these connections to multiple description, we hope to motivate a solution to what remains a mostly unsolved problem.

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Copyright © 2007 IEEE. Reprinted from IEEE Transactions on Information Theory.

Danlu Zhang, Seong-Jun Oh, and Naga Bhushan

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.

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Copyright © 2007 IEEE. Reprinted from IEEE Transactions on Wireless Communications.

Wanshi Chen, Michael J. Neely and Urbashi Mitra

This paper focuses on energy-efficient packet transmission with individual packet delay constraints. The optimal offline scheduler (vis-`a-vis total transmission energy), assuming information of all packet arrivals before scheduling, was developed by Zafer, et al. (2005) and Chen et al. (2006). This paper shows that when packet inter-arrival times are identically and independently distributed (i.i.d.), the resulting optimal transmission durations of packets m and M−m+1, m ∈ [1, · · · ,M],M ≥ 1, are identically distributed. This symmetry property leads to a simple and exact solution of the average packet delay under the optimal offline schedule. Two heuristic online scheduling algorithms, which assume no future arrival information, are then studied. These online schedulers are compared with the optimal offline scheduler in terms of delay and energy performance via analysis and simulations. While both online schedulers are inherently inferior, one online scheduler is shown to achieve a comparable energy performance to the optimal offline scheduler in a wide range of scenarios.

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Copyright © 2007 IEEE. Reprinted from IEEE Infocom 2007.

Yibo Jiang, Alexei Ashikhmin, Ralf Koetter, and Andrew C. Singer

In this paper, we study moments of soft bits of binary-input symmetric-output channels and solve some extremal problems of the moments.We use these results to solve the extremal information combining problem. Further, we extend the information combining problem by adding a constraint on the second moment of soft bits, and find the extremal distributions for this new problem. The results for this extension problem are used to improve the prediction of convergence of the belief propagation decoding of low-density parity-check (LDPC) codes, provided that another extremal problem related to the variable nodes is solved.

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Copyright © 2008 IEEE. Reprinted from IEEE Transactions on Information Theory.

Vinay Sridhara Hweechul Shin Stephan Bohacek

Signal to interference plus noise ratio, SINR, is one of the main factors that affects the quality of wireless communication. While the impact of white Gaussian noise on a wireless channel is well understood, impact of interference remains one of the less explored areas. With the deployment of dense mesh networks, the interference will be a dominant factor that affects the transmission errors. This paper explores the performance of 802.11b/g when subject to interference. The findings are based on various controlled experiments in the laboratory setting. One finding of this work is that in contrast to communication over links where the noise is Gaussian, in 802.11b/g, the probability of successfully transmitting a packet is dominated by the ability of the receiver to synchronize with the carrier. As a result, changing to a lower bit-rate with same synchronization scheme will not make the transmission more resilient to interference. The significance of this result on bitrate selection is briefly explored.

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Copyright © 2007 IEEE. Reprinted from Computer Communications and Networks, proceedings of 16th International Conference on