Simon Armour

Green radio: radio techniques to enable energy-efficient wireless networks

Recent analysis by manufacturers and network operators has shown that current wireless networks are not very energy efficient, particularly the base stations by which terminals access services from the network. In response to this observation the Mobile Virtual Centre of Excellence (VCE) Green Radio project was established in 2009 to establish how significant energy savings may be obtained in future wireless systems. This article discusses the technical background to the project and discusses models of current energy consumption in base station devices. It also describes some of the most promising research directions in reducing the energy consumption of future base stations.

A comparison of the HIPERLAN/2 and IEEE 802.11a wireless LAN standards

At present, WLANs supporting broadband multimedia communication are being developed and standardized around the world. Standards include HIPERLAN/2, defined by ETSI BRAN, 802.11a, defined by the IEEE, and HiSWANa defined by MMAC. These systems provide channel adaptive data rates up to 54 Mb/s (in a 20 MHz channel spacing) in the 5 GHz radio band. An overview of the HIPERLAN/2 and 802.11a standards is presented together with software simulated physical layer performance results for each of the defined transmission modes. Furthermore, the differences between these two standards are highlighted (packet size, upper protocol layers etc.), and the effects of these differences on throughput are analyzed and discussed.

Hotspot wireless LANs to enhance the performance of 3G and beyond cellular networks

At present, WLANs supporting broadband multimedia communications are being developed and deployed around the world. Standards include HIPERLAN/2 defined by ETSI BRAN and the 802.11 family defined by the IEEE. These systems provide channel adaptive data rates up to 54 Mb/s (in a 20 MHz channel spacing) over short ranges up to 200 m. The HIPERLAN/2 standard also specifies a flexible radio access network that can be used with a variety of core networks, including UMTS. It is likely that WLANs will become an important complementary technology to 3G cellular systems and will typically be used to provide hotspot coverage. In this article the complementary use of WLANs in conjunction with UMTS is presented. In order to quantify the capacity enhancement and benefits of cellular/hotspot interworking we have combined novel ray tracing, software-simulated physical layer performance results, and optimal base station deployment analysis. The study focuses on an example deployment using key lamppost mounted WLAN access points to increase the performance (in terms of capacity) of a cellular network.

Adaptive frequency-domain equalization for single-carrier multiple-input multiple-output wireless transmissions

Channel estimation and tracking pose real problems in broadband single-carrier wireless communication systems employing multiple transmit and receive antennas. An alternative to estimating the channel is to adaptively equalize the received symbols. Several adaptive equalization solutions have been researched for systems operating in the time domain. However, these solutions tend to be computationally intensive. A low-complexity alternative is to adaptively equalize the received message in the frequency domain. In this paper, we present an adaptive frequency-domain equalization (FDE) algorithm for implementation in single-carrier (SC) multiple-input multiple-output (MIMO) systems. Furthermore, we outline a novel method of reducing the overhead required to train the proposed equalizer. Finally, we address the issues of complexity and training sequence design. Other computationally efficient adaptive FDE algorithms for use in SC systems employing single transmit and receive antennas, receive diversity, or space-time block codes (STBC) can be found in the literature. However, the algorithm detailed in this paper can be implemented in STBC systems as well as in broadband spatial multiplexing systems, making it suitable for use in high data rate MIMO applications.

Joint Time-Frequency Domain Proportional Fair Scheduler with HARQ for 3GPP LTE Systems

This paper explores the potential gain of joint diversity in both frequency domain and time domain which can be exploited to achieve spectral efficiency gains whilst simultaneously facilitating QoS/fairness in an OFDMA system (particularly in 3GPP Long Term Evolution (LTE)). The performance of several joint time-frequency schedulers is investigated. Simulation results show that joint time frequency schedulers achieve significantly superior performance compared to a more conventional time domain (only) proportional fair scheduler. The joint schemes show promising throughput gain while meeting stringent fairness criteria.

Performance Evaluation of Hybrid ARQ Schemes of 3GPP LTE OFDMA System

Expectations and requirements for future wireless communication systems continue to grow and evolve. Thus, recently, the third generation partnership project (3GPP) has considered the long term evolution (LTE) of 3G - also known as super 3G - to ensure its competitiveness in the future. It is generally assumed that the downlink of the new air interface would be OFDMA based and that some form of hybrid ARQ (HARQ) might be employed. This paper aims to evaluate the performance of various HARQ schemes over the OFDMA downlink of the currently proposed 3GPP LTE specification. Schemes are compared in terms of throughput and PER in the context their differing memory requirements for implementation. Simulation results show that type II incremental redundancy offers the best throughput performance but at the cost of higher memory requirement. However, when the schemes are enhanced with subcarrier and constellation rearrangement techniques, the performance gap between the different HARQ types is reduced significantly.

A comparison of HIPERLAN/2 and IEEE 802.11a physical and MAC layers

At present, wireless local area networks (WLANs) supporting broadband multimedia communication are being developed and standardized. Two such standards are HIPERLAN/2, defined by ETSI BRAN and the IEEEs 802.11a. These WLAN standards will provide data rates up to 54 Mbps (in a channel spacing of 20 MHz) in the 5.2 GHz band. In this paper, an overview of the the standards is presented together with software simulated physical layer performance results for each of the transmission modes defined in the two standards. Furthermore, the differences between the standards (protocol data unit-PDU-size, upper protocol layers etc.) and the effects on applications are discussed.

Decision feedback equalization in SC-FDMA

SC-FDMA (Single-Carrier Frequency Division Multiple Access) is employed in the 3GPP LTE (Long-Term Evolution) standard as the uplink transmission scheme. The SC-FDMA signal has a low PAPR. This makes it well-suited to power efficient transmission at the mobile terminal. Although it is a common assumption to use frequency-domain linear equalization in SC-FDMA, a decision feedback equalizer (DFE) composed of a frequency-domain feedforward filter and a time-domain feedback filter can provide enhanced performance. Even when error propagation is taken into account, results show that a DFE still offers a significant performance gain over the conventional LE for uncoded SC-FDMA. This paper demonstrates that SC-FDMA with DFE is capable of increasing the throughput in a power limited channel by up to 41% compared to LE. Alternatively, for a given peak transmit power, the use of a DFE can achieve a 14% coverage extension in NLOS and 19% in LOS.

Design Considerations and Physical Layer Performance Results for a 4G OFDMA System Employing Dynamic Subcarrier Allocation

In this paper the key design considerations and link parameters for a 4G coded OFDMA system are identified and physical layer performance results are presented for a number of transmission modes. Additionally, this paper investigates the problem of dynamic multiuser subcarrier allocation in a coded OFDMA system. A novel, near-optimal, low complexity algorithm is proposed that attempts to exploit multiuser diversity by allocating sub-carriers to users so as to achieve substantial increases in perceived channel gain which are approximately equal for all users. Performance results show that performance is significantly enhanced when this algorithm is employed. Gains up to 10 dB can be observed

A channel estimation algorithm for MIMO-SCFDE

This letter proposes a novel method for channel estimation in a single-carrier multiple input-multiple output (MIMO) system with frequency-domain equalization/detection. To this end, we construct novel short MIMO training sequences that have constant envelope in the time domain to preclude the peak-to-average power ratio problem encountered in many systems that utilize the frequency domain for data recovery. Simultaneously, the spectrum in the frequency domain is flat except for a grid of nulls for predefined frequency tones. Armed with these sequences, we provide an algorithm that is optimal in the least squares (LS) sense at a potentially low computational cost. Results show that the algorithm performs identically to other proposed LS techniques. Furthermore, the algorithm is extremely bandwidth efficient in that the total training overhead required to obtain full CSI is just one block.