Time-efficient resource allocation algorithm over HSDPA in femtocell networks

Abstract

This paper presents a time-efficient optimal resource allocation algorithm aiming to maximize the system throughput of the single-user High Speed Downlink Packet Access (HSDPA) deployed in a femtocell base station. The system throughput maximization with constrained total power is formulated as a constrained integer programming problem. We first prove that a two-group bit and energy allocation provides the global optimum solution in the system without multipath. We then focus on the use of the two-group allocation method over frequency selective channels. A pre-processing method was used to systematically cluster and remove channels to prevent using energies over severely degraded channels with the two-group allocation approach. This improves the system throughput whilst greatly reducing the computation complexity. The proposed twogroup approach with channel removal is suitable for femtocell base station with limited signal processing capability.

The interference-reduced energy loading for multi-code HSDPA systems

“…Recently, an iterative power adaptation method known as the two-group resource allocation scheme has been developed in [30,31] to load two distinct discrete bit rates over the multi-code downlink channels subject to a constrained total transmission power. The twogroup resource allocation scheme [30,31] is integrated into the system value based power allocation method with the SIC scheme to improve the total downlink bit rate for a single user. In the following section a system model is given for the constrained optimization formulation when maximizing the total rate for multi-code downlink transmissions.…”

“…The (N + L-1) × K dimensional matrix W = w 1 , ..., w k , ..., w K has the MMSE linear equalizer despreading filter coefficients w K for k = 1,..., K. To ensure that w H k q k = 1 while minimizing the cross-correlations w H k q j for j ≠ k, a normalized MMSE despreading filter coefficient vector [30],…”

Successive interference cancellation for two-group resource allocation

“…To fully utilize the constrained energy, the code channels may be divided into two groups [2], each of which is allocated a distinct adjacent bit rate per channel. With a smaller set of realizable bit rates having large granularities, which are the differences between the adjacent bit rates, this scheme has been demonstrated to achieve better performance with a relatively lower complexity as compared to the existing loading schemes [3], which allocate an equal bit rate to each code channel.…”

“…Although the same iterative calculation technique can be incorporated for the two-group algorithm [2] to efficiently utilize the total energy and improve the total transmission bit rate, the computational load incurred by this iterative technique is prohibitively high. The matrix inversions required in the calculation process to adopt the minimum mean square error (MMSE) technique [4] for minimizing multiple access inter ference (MAl) and noise components significantly increase the computational load.…”

“…Although the presence of MAl and lSI were assumed, the cross-correlations between different signature sequences at the receiver end were assumed to be constant and equal for all code channels, which may not be the case in practice. In this paper, a different SIC-based energy allocation scheme [10], which requires a relatively low computational load without matrix inversions to mitigate lSI and MAl components and enhance the total transmission bit rate, is proposed and in tegrated with the two-group resource allocation scheme [2]. A packet-based detection scheme known as the coded parity packet (CPP) coding scheme [11] is also combined with this proposed loading scheme to provide correctly detected previous and next symbols from the packet received in the currently detected channel for the SIC and detection operations on the packet in the next channel.…”