Stephen Grant

Per-antenna-rate-control (PARC) in frequency selective fading with SIC-GRAKE receiver

In this paper we consider a generalization of the per-antenna-rate-control (PARC) MIMO scheme for the HSDPA option of WCDMA. The scheme, called PARC-N, allows the number of transmitted data substreams N to be less than the number of transmit antennas M and selects the best N antennas for transmission. We investigate PARC-N specifically in frequency selective fading environments. First, we develop a novel receiver structure that combines successive interference cancellation (SIC) with generalized-RAKE technology that achieves a good balance between performance and complexity. We then draw several interesting conclusions: (1) data throughput can be maximized by using N /spl les/ M, where N may be adaptively selected based on operating conditions; (2) data throughput is maximized by allocating all non-data signal power (pilots, voice, overhead, etc.) to as few transmit antennas as possible; and (3) the use of pilot subtraction at the receiver is much more beneficial in MIMO systems than in single-antenna or receive diversity systems.

High Speed Packet Access Evolution - Concept and Technologies

In this paper we present the main concepts of high speed packet access evolution currently being standardized in 3GPP. In general HSPA evolution consists of introduction of MIMO, higher order modulation, and protocol optimizations and optimizations for voice over IP. We describe these improvements in detail and show that HSPA Evolution can reach performance comparable to those of long term evolution of UMTS terrestrial radio access network in a 5 MHz deployment.

Load control for multi-stage interference cancellation

Multi-stage interference cancellation (IC) can improve the interference conditions for all users of a cell. In order to exploit the IC gain at system level, it is important to design radio resource management algorithms that account for this gain. For this purpose, two new load control algorithms are proposed in this paper, together with some further enhancements. For Algorithm 1, load control and scheduling are still performed based on the air interface Rise over Thermal (RoT), but with an increased RoT target. The RoT target is determined based on the estimated IC gain. A cell-specific and dynamic RoT target is hence used rather than a constant one. With Algorithm 2, load control and scheduling are performed based on an effective RoT without increasing the RoT target. The load control function is placed after an intermediate IC stage depending on the timing constraints and/or the required IC processing gain of the coverage limiting channels. With the proposed algorithms, system-level simulation results show that the average cell throughput can be considerably improved and at the same time the coverage can be maintained at a level similar to a system without IC.

Reference Signals for Improved Energy Efficiency in LTE

Cellular wireless systems have focused, to date, on system capacity, user data rates, latency and coverage as primary design criteria. Energy efficiency has recently received increased attention as another important criterion to be considered. The potential for energy savings in 3GPP LTE systems has been investigated in [1]-[3]. An important design element that determines the potential for energy efficient transmission is the structure of reference signals that need to be transmitted independent of the load in the network, such as the cell-specific reference signals (CRS) in 3GPP LTE systems. This paper discusses modifications to the reference signal structure in LTE that can enable greater energy efficiency. The time and frequency estimation performance implications of such modifications are evaluated and discussed.

Optimal and reduced complexity receivers for MISO antenna systems

MISO antenna systems employing feedback of the downlink channel state are attractive for achieving diversity in the downlink of cellular systems. In this paper we consider a particular MISO transmit diversity scheme with rich feedback (TDRF), and derive the optimal receiver structure taking into account intersymbol interference, colored noise, and the self-interference from pilot signals used for downlink channel estimation. We then compare the bound on performance established by the optimal receiver with the performance of a low complexity alternative consisting of a fixed receive filter followed by a sampler. Our results show that the application of TDRF to the WCDMA downlink gives substantial gains compared to a single antenna system, even when the extremely simple sampler receiver is used at the mobile terminal.