Oliver Holland

Cross-Layer Optimization to Maximize Fairness Among TCP Flows of Different TCP Flavors

A significant body of recent research has analyzed the problematic behavior of TCP over wireless links, and a plethora of modifications to TCP have been proposed in order to increase its performance in such contexts. Two schools of thought have emerged: the first proposes changes to the end-to- end protocol, while the second explores the potential to enhance lower layers as a means to improve the end-to-end performance of TCP. This paper focuses on the latter, and in contrast to most research in this area, which thus-far has concentrated on a single TCP flavor, examines the case where different TCP flavors are competing over a wireless link. To this end, we present and assess a cross-layer solution that involves the adaptation of lower layer characteristics (i.e., the coding rate) based on the detected TCP flavor, in order to maximize the fairness among TCP flows. Through extensive numerical investigations, we show that the proposed scheme considerably improves the fairness over wireless links among different TCP flavors. Our approach also has a minimal effect on the aggregate throughput of the TCP flows, and in cases where the packet error rate is very low, has a small positive effect on throughput.

Architecture and enablers for optimized radio resource usage in heterogeneous wireless access networks: The IEEE 1900.4 Working Group

Over the past decade or so, the wireless industry has undergone many significant changes. Radio systems have moved toward forming heterogeneous wireless networks: collaborations of multiple radio access networks, which in some cases operate different radio access technologies, such as second- and third-generation cellular RATs, IEEE 802.x wireless standards, and so on. On the other hand, multimode reconfigurable user devices with the ability to choose among various supported RATs have become a reality, and devices and networks with dynamic spectrum access capabilities, allowing real-time sharing of spectrum resource usage among different systems, are expected to be a part of the future radio eco-space. As a result of these changes, there is a need to develop a standard that addresses the requirements and leverages the opportunities posed by such a versatile radio environment. To this end, IEEE 1900.4 aims to standardize the overall system architecture and information exchange between the network and mobile devices, which will allow these elements to optimally choose from available radio resources. In other words, the standard facilitates the distributed dynamic optimization of the usage of spectrum offered by the heterogeneous wireless network, relying on a collaborative information exchange between networks and mobile devices, thereby acting as a common means to improve overall composite capacity and quality of service for the served networks. This article provides a snapshot of IEEE P1900.4 in its current form, covering the scope and purpose of the standard, reference use cases for which the standard is applicable, its system and functional architectures, and finally, the information model for its main interfaces.

Interference-limited resource allocation for cognitive radio in orthogonal frequency-division multiplexing networks

Efficient and fair resource allocation strategies are being extensively studied in current research in order to address the requirements of future wireless applications. A novel resource allocation scheme is developed for orthogonal frequency-division multiplexing (OFDM) networks designed to maximise performance while limiting the received interference at each user. This received interference is in essence used as a fairness metric; moreover, by defining different interference tolerances for different sets of users, the proposed allocation scheme can be exploited in various cognitive radio scenarios. As applied to the scheme, the authors investigate a scenario where two cellular OFDM-based networks operate as primary and secondary systems in the same band, and the secondary system benefits by accessing the unused resources of the primary system if additional capacity is required. The primary system benefits either by charging the secondary system for the use of its resources or by some form of reciprocal arrangement allowing it to use the secondary systems licenced bands in a similar manner, when needed. Numerical results show our interference-limited scheduling approach to achieve excellent levels of efficiency and fairness by allocating resources more intelligently than proportional fair scheduling. A further important contribution is the application of sequential quadratic programming to solve the non-convex optimisation problems which arise in such scenarios.

A Comparison Between the Centralized and Distributed Approaches for Spectrum Management

There is a growing demand for spectrum to accommodate future wireless services and applications. Given the rigidity of current allocations, several spectrum occupancy studies have indicated a low utilization over both space and time. Hence, to satisfy the demands of applications it can be inferred that dynamic spectrum usage is a required necessity. Centralized Dynamic Spectrum Allocation (DSA) and Distributed Dynamic Spectrum Selection (DSS) are two paradigms that aim to address this problem, whereby we use DSS (distributed) as an umbrella term for a range of terminologies for decentralized access, such as Opportunistic Spectrum Access and Dynamic Spectrum Access. This paper presents a survey on these methods, whereby we introduce, discuss, and classify several proposed architectures, techniques and solutions. Corresponding challenges from a technical point of view are also investigated, as are some of the remaining open issues. The final and perhaps most significant contribution of this work is to provide a baseline for systematically comparing the two approaches, revealing the pros and cons of DSA (centralized) and DSS (distributed) as methods of realizing spectrum sharing.

A Universal Resource Awareness Channel for Cognitive Radio

Cognitive radio is certain to transform our traditional radio resource allocation regimes. Through cognitive radio, better spectrum efficiency can be leveraged by radios intelligently altering their radio resource usages dependent on locally available information about radio conditions. A significant challenge for cognitive radio, however, is awareness of these local radio conditions. One crude solution is for the radio to periodically scan the complete spectrum band over which cognition in radio resource usages can apply. Such an operation would be time-consuming and wasteful of power, and ultimately would be entirely impractical. In this paper, we therefore propose the concept of a resource awareness channel (RAC)-a single universally available channel on a fixed frequency, on which information about resource usage is conveyed by all radios using the cognitive radio spectrum band. This allows cognitive radios that want to alter their transmission resources to make an informed decision about the practicality or these prospective changes in terms or interference for the system as a whole, simply by listening to the RAC. We analyse the performance or this proposed RAC concept, and show it to be practical even in areas that are highly populated by radios

Spectrum Power Measurements in 2G and 3G Cellular Phone Bands During the 2006 Football World Cup in Germany

This contribution presents spectrum occupancy measurements which have been performed during the 2006 Football World Cup in Germany, in the cities of Kaiserslautern and Dortmund. The measurements investigate the time-variation of powers in 2G bands (900 MHz and 1800 MHz), a spectrum bandwidth including 3G bands and an ISM band (2000- 2600 MHz), and a global band (400-2600 MHz), on the day prior to a match, the day of the match, and during the match. The first intention is to study changes in power levels and subsequently relate this to specific events, such as (i) the start of the match, (ii) half-time, and (Hi) the end of the match. A next intention is to investigate the autocorrelation structure of changes in power levels, and relate this to the ease with which dynamic spectrum allocation might be performed. The results that ensue are used to inspire a discussion as to how dynamic spectrum allocation and short-range localized solutions such as IEEE 802.11 basestations might be leveraged to bolster capacity at large-scale events.

To white space or not to White Space: That is the trial within the Ofcom TV White Spaces pilot

TV White Space (TVWS) has taken a big step forward with the UK regulator Ofcom initiating a pilot of the technology in the UK, based on rules for White Space Devices (WSDs) standardized and harmonized at the European level by ETSI. This paper reports on a subset of the work undertaken by our large-scale trial within the Ofcom Pilot, investigating what is achievable in TVWS in terms of availability and capacity, and strongly focusing on the potential to aggregate white space resources. Moreover, this paper provides some experimental results and observations from our trial, particularly around issues such as performance testing and assessment of appropriate scenarios for TVWS deployments. Some of the key observations in this paper, among numerous others, include: (i) In the UK, it seems likely that TVWS has most performance/benefit potential in below-rooftop receiver and indoor/underground deployments. For availability and capacity analyses, we particularly define and assess TVWS scenarios that we term as “mobile broadband downlink” and “indoor wireless local-area networking” based on this realization. We further demonstrate the strength of TVWS for indoor communications through a range of challenging experiments inside the Strand Campus of Kings College London. (ii) There is ample TVWS available in much of the UK and particularly in the London area, although this is affected greatly by the scenario that is considered and can be very highly variable. The mobile broadband downlink scenario is particularly affected by availability reduction and variability outside of the London area. Impressive capacities can be achieved by optimal aggregation in TVWS. Achievable area capacity in TVWS is high. (iii) In a number of cases, and particularly under some aggregation scenarios, subsets or indeed all WSD spectrum mask classes give similar performance. (iv) A worst case 700 MHz spectrum reassignment for ITU Region 1 in WRC 2015 could significantly affect availability/capacity in some TVWS usage scenarios, for lower quality spectrum mask class WSDs.

Cognitive radio for medical body area networks using ultra wideband

Wearable wireless medical sensors beneficially impact the healthcare sector, and this market is experiencing rapid growth. In the United States alone, the telecommunications services market for the healthcare sector is forecast to increase from

SACRP: A Spectrum Aggregation-Based Cooperative Routing Protocol for Cognitive Radio Ad-Hoc Networks

7.5 billion in 2008 to

Development of a Radio Enabler for Reconfiguration Management within the IEEE P1900.4 Working Group

11.3 billion in 2013. Medical body area networks improve the mobility of patients and medical personnel during surgery, accelerate the patients¿ recovery, and facilitate the remote monitoring of patients suffering from chronic diseases. Currently, MBANs are being introduced in unlicensed frequency bands, where the risk of mutual interference with other electronic devices can be high. Techniques developed during the evolution of cognitive radio can potentially alleviate these problems in medical communication environments. In addition, these techniques can help increase the efficiency of spectrum usage to accommodate the rapidly growing demand for wireless MBAN solutions and enhance coexistence with other collocated wireless systems. This article proposes a viable architecture of an MBAN with practical CR features based on ultra wideband radio technology. UWB signals offer many advantages to MBANs, and some features of this technology can be exploited for effective implementation of CR. We discuss the physical and MAC layer aspects of the proposal in addition to the implementation challenges.