John Edward Smee

Multicell downlink capacity with coordinated processing

We study the potential benefits of base-station (BS) cooperation for downlink transmission in multicell networks. Based on a modified Wyner-type model with users clustered at the cell-edges, we analyze the dirty-paper-coding (DPC) precoder and several linear precoding schemes, including cophasing, zero-forcing (ZF), and MMSE precoders. For the nonfading scenario with random phases, we obtain analytical performance expressions for each scheme. In particular, we characterize the high signal-to-noise ratio (SNR) performance gap between the DPC and ZF precoders in large networks, which indicates a singularity problem in certain network settings. Moreover, we demonstrate that the MMSE precoder does not completely resolve the singularity problem. However, by incorporating path gain fading, we numerically show that the singularity problem can be eased by linear precoding techniques aided with multiuser selection. By extending our network model to include cell-interior users, we determine the capacity regions of the two classes of users for various cooperative strategies. In addition to an outer bound and a baseline scheme, we also consider several locally cooperative transmission approaches. The resulting capacity regions show the tradeoff between the performance improvement and the requirement for BS cooperation, signal processing complexity, and channel state information at the transmitter (CSIT).

Downlink Macro-Diversity in Cellular Networks

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 > N² regime, it coincides with the ZF precoder, while, in the SNR < N² regime, 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.

Implementing interference cancellation to increase the EV-DO Rev A reverse link capacity

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.

Distributed Beamforming Based on Signal-to Caused-Interference Ratio

This paper presents a distributed beamforming technique that addresses the effect of inter-cell interference on the downlink of cellular communications systems. The beamforming weights are computed in a distributed manner at each transmit sector antenna array without the need for inter-sector communication. The beamforming weights are chosen to compromise between maximizing the power to the served user from each sector while minimizing the interference caused to users served in adjacent sectors. The extensions of this method for variable levels of channel state information feedback and multiple receiver antennas are introduced. Beamforming codebooks with power variations across antennas are presented. We show how users can additionally feed back the fraction of interference caused by each interfering sector to incorporate the urgency of interference avoidance into the transmitter optimization.

WLC04-4: Network Performance of the EV-DO CDMA Reverse Link with Interference Cancellation

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.

Receiver Architectures and Design Tradeoffs for CDMA Interference Cancellation

This paper investigates the design of commercially viable CDMA basestation receivers that incorporate interference cancellation. Results are given for cdma2000 1xEV-DO but also apply to WCDMA HSUPA. The effect of receiver memory size is determined for canceling packets transmitted with hybrid-ARQ. Performance-complexity tradeoffs are presented for implementing iterative and successive interference cancellation of asynchronous user transmissions. Multipath channel estimation techniques of varying complexity are compared based on sector throughput. Practical interference cancellation designs with moderate complexity are shown to achieve a large fraction of the gains of more elaborate techniques.

On the reverse link performance of the cdma2000 1xEV-DO revision A system with antenna array receivers

cdma2000 1xEV-DO revision A (DO Rev. A), also known as IS-856-A, is a third generation (3G) wireless solution to providing wide-area high-speed mobile Internet access with high spectral efficiency and advanced quality-of-service (QoS) support. In this paper we evaluate the reverse link performance improvement (in terms of coverage and data throughput) of IS-856-A with the use of more advanced antenna array receivers. Specifically, we consider the effect of increasing the receiver antenna array size and utilizing more sophisticated beamforming schemes. We quantify the capacity improvement via analysis as well as comprehensive system simulations that incorporate realistic channel models and the dynamics associated with MAC-layer algorithms in addition to the physical-layer interactions. We show that DO Rev. A with 4-way antenna diversity on the reverse link achieves more than 3 dB gain over 2-way diversity receivers in sector throughput. We also demonstrate a coverage improvement on the order of 6 dB, which can be translated into further throughput gains by relaxing the interference control mechanism

5G ultra-reliable and low-latency systems design

5G New Radio (NR) is envisioned to support three broad categories of services: evolved mobile broadband (eMBB), ultra-reliable and low-latency communications (URLLC), and massive machine-type communications (mMTC). The URLLC services refer to future applications that require secure data communications from one end to another with ultra-high reliability and deadline-based low latency requirements. This type of quality-of-service is vastly different from that of traditional mobile broadband applications. In this paper, we discuss the systems design principles to enable the URLLC services in 5G. Theoretical queueing analysis and system-level simulations are provided to support these systems design choices, many of which have been considered as work items in the 3GPP Release 15 standards, which will be the first release for 5G NR.

WLC08-5: Link-Level Modeling and Performance of CDMA Interference Cancellation

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.

Implementing CDMA Reverse Link Interference Cancellation

We describe ongoing research and product development focused on the theory, system design, and capacity gains from incorporating reverse link interference cancellation into commercial CDMA basestations. The work considers receiver architecture design tradeoffs, link cancellation efficiency in multipath fading channels, and the multi-cell network operation and performance