Sean M. McBeath

Efficient Signaling for VoIP in OFDMA

Voice over Internet protocol (VoIP) will be commonplace in future wireless standards. Due to the potentially large number of VoIP users in a wireless system, the overhead associated with controlling VoIP transmissions can hinder system performance, unless it is carefully managed. This paper outlines current efforts in B3G (beyond 3G) standards development to efficiently control VoIP transmissions by grouping VoIP users into scheduling groups, assigning the group a set of shared time-frequency resources, and using bitmap signaling to allocate resources. System level simulations are used to validate the signaling technique and show that the technique can efficiently support 93 users per megahertz. Potential further improvements are described.

Link-to-system mapping techniques using a spatial channel model

Computer simulations are often used to predict the performance of cellular networks. Typically, link level simulators are used to model the link between the base and mobile station, while system level simulators model the entire network. To most accurately predict the performance of cellular networks, a system level simulator, which includes the performance of the link between each base and mobile station, should be used. Unfortunately, the computational complexity of such simulators makes this impractical. An alternative technique consists of separately simulating the link and system components with an interface or mapping to combine the results. Link-to- system mapping techniques have been defined in the past for this purpose, but only for a few specific channel models. With recently developed channel models, such as the spatial channel model (SCM), a random channel is generated for each user, which makes it impossible to have separate link level results for each channel realization used in the system level simulator. This paper presents two link-to-system mapping techniques that produce consistent results for a wide range of SCM channel realizations. The techniques are illustrated using the 3GPP2 Forward Packet Data Channel of 1xEV-DV and the Forward Traffic Channel of 1xEV-DO.

W-CDMA power amplifier modeling

This paper discusses a simple yet accurate approach for modeling W-CDMA power amplifiers. Several stages of the modeling process are presented. First, the test signals are defined. W-CDMA signals are approximated using simple periodic signals. These signals are then used as inputs to the power amplifier (PA) measurement system. Second, a process for deriving the AM/AM and AM/PM characteristics is given. The AM/AM and AM/PM characteristics, which are derived directly from the measured PA data, are used as the basis for modeling. The tapped-delay-line (TDL) model is used to model the AM/AM and AM/PM characteristics. The TDL model is accurate to -40 dB when linear filters are inserted before and after the AM/AM and AM/PM characteristics are modeled.

Applying the convex metric and the spatial channel model for HRPD rev-A

Computer simulations are often used to predict the performance of cellular networks. Typically, link level simulations are used to model the link between the access network (AN) and the access terminal (AT), while system level simulations are used to model a system consisting of many ANs and ATs. Since completely modeling the link between each AN and AT is impractical within system level simulators, link-to-system mapping techniques are used to incorporate link level behavior into system level simulators. The Equivalent SNR Method Based on Convex Metric (ECM) is one link-to-system mapping technique, which has been shown to produce accurate results for many different cellular systems. In this paper, we further examine the ECM by showing its performance for the Forward Traffic Channel (F- TCH) defined in the cdma2000  High Rate Packet Data (HRPD) Air Interface Specification. In particular, we show that the ECM produces consistent results for the F-TCH using the unique characteristics of the spatial channel model (SCM). We further show that the ECM is valid for simulating the HRPD early termination algorithm, a type of incremental redundancy.

Impact of imperfect estimators on W-CDMA receiver performance with MIMO antenna systems

Multiple-input multiple-output (MIMO) antenna systems have been proposed to enhance the capabilities of the high-speed downlink-shared channel (HS-DSCH) of WCDMA. To date, link simulations have been used to demonstrate the performance of this system. However, these studies have generally relied upon ideal solutions for determining the channel impulse response, minimum mean-squared-error (MMSE) filter coefficients, and SINR. In this paper, we present practical solutions for estimating the channel, MMSE filter coefficients, and SINR, and then compare the link level performance using ideal solutions to that with estimated solutions.

Digital memory-based predistortion

A predistortion algorithm based on a memory-based power amplifier model (PA) is presented. The algorithm was tested using a PA measurement system. The predistortion techniques are based on the filtered tapped delay line (TDL) model. Memoryless predistortion techniques are also presented to show the benefits of the memory-based predistortion approach. Memoryless predistortion reduces third order IM by 5-8 dB, while memory-based predistortion reduces third order IM by 18-20 dB.

Multiple User Packet Repackaging

Revision A of the cdma2000 High Rate Packet Data (HRPD) Air Interface Specification includes a method to serve multiple users in a single packet (3GPP2, 2004), This method is know as medium access control (MAC) layer multiplexing and can facilitate up to 8 users in one packet. It allows Revision A of HRPD to be more effective, when compared to previous revisions of HRPD, in delivering real time applications such as voice, video, and gaming due to the latency improvement. This paper examines the impact on system capacity that results from a proposed technique whereby MAC layer multiplexed transmissions can be terminated prematurely once a certain number of the target receivers have successfully decoded the transmission. It was found that system capacity could be improved by up to 5.8%.

Multi-antenna systems for the cdma2000/spl reg/ F-PDCH

Several multiple antenna technologies have been proposed in various forms to the 3GPP2 standards body for the 1xEV-DV (1x EVolution for Data and Voice) standard. While open loop transmit diversity has been standardized for the fundamental and supplemental channels, no multiple antenna scheme has been standardized for the packet data channel. Therefore, it is important to understand the performance benefits of multiple antennas for the forward packet data channel (F-PDCH) of 1xEV-DV. This document provides a comparison of several multiple antenna technologies from an information theory perspective and through link level simulations. In addition, the performance benefits of minimum mean squared error (MMSE) equalizers are discussed. It is shown that open loop diversity schemes provide marginal gain over single antenna systems, while closed loop diversity systems provide significant gains. Further, it is shown that MMSE equalizers provide significant gains for multi-path channels.

WLC09-4: System Level Performance of HRPD Revision B

Revision B of the high rate packet data standard defines several new transmission formats for forward traffic channel transmission. The new transmission formats provide higher order modulation, an increased quantization in nominal data rate, and more opportunity for hybrid automatic repeat request gain. Consequently, the access terminal has many more choices when mapping a measured pilot signal-to-noise ratio to a requested transmission format. Ultimately, the new transmission formats result in a more efficient use of system resources leading to increased system performance. In this paper, we show that system level performance is increased by 25% for one receive antenna and 28% for two receive antennas as a result of the new transmission formats. We further show the distribution of selected transmission formats.