Packet error statistics of LOS broadband fixed wireless access channels

This paper uses a detailed site-specific channel model to analyze the impact of path loss and co-channel interference (CCI) in a multi-base station broadband fixed wireless access (BFWA) network. The base stations are deployed in an urban setting and make use of sectorised multi-element arrays to suppress CCI from other cells/sectors. Customer premises equipment (CPE) is mounted at rooftop level on a number of surrounding buildings. Spatially correlated multiple input multiple output (MIMO) channels are produced for each link using channel data generated from the ray-tracing model. The tool predicts MIMO correlation based on radiowave propagation and antenna array geometries. The paper considers the use of uniform linear arrays (ULA) and Uniform circular arrays (UCA) with a number of different element spacings. The results provide a unique insight into the deployment of multi-element WiMAX networks in an urban setting.

We present flow-level upstream traffic behavior based on data collected from broadband fixed wireless (BFW) and digital subscriber line (DSL) access services. The study involves data collected using Cisco's NetFlow tools on both access networks. The observations indicate that a number of applications based on peer-to-peer (P2P) concepts create most of the upstream traffic. The flows observed are mostly short-lived for both BFW and DSL access, with DSL being the lesser of the two. The inter-arrival time displays near-range correlation for the DSL flows. There is a significant periodicity observed in the interarrival time distribution for flows on BFW access, which is indicative of the influence of the underlying medium access control (MAC) protocol on traffic behavior. These analysis of upstream traffic characteristics form the first step towards constructing a generalized parametric model for broadband access networks.

Video is expected to be the dominant application by traffic volume over mobile networks in the near future. Mobile network operators are deploying video optimization techniques to enhance the user experience and network utilization for video delivery. Video optimization is typically “out-of-network” and includes techniques such as transcoding, transrating, time shifting and pacing that are implemented outside of mobile radio access and core networks. However, such techniques cannot easily exploit information about real time cell congestion and radio conditions for the video terminals because it is difficult to obtain such information from the radio access network. We propose a novel “in-network” video optimization technique, named Adaptive Guaranteed Bit Rate (AGBR), for HTTP-based Adaptive Streaming (HAS) video. This optimization technique is implemented at the base station and can thus exploit knowledge of the radio and congestion conditions. With only limited knowledge of the video stream properties or content, AGBR works by adjusting the throughput delivered to the different HAS clients that in turn adjust the video quality they request. The optimization algorithm maximizes aggregate quality across multiple video flows served by the base station without starving data clients, thereby improving the overall quality of experience. We demonstrate through extensive analytical modeling and simulations that AGBR can adapt to changing network conditions to support more video sessions at an acceptable quality than alternative algorithms, while enforcing fairness among all users competing for resources within a sector.

We investigate the use of a multi-element antenna array (MEA) at the base station (BS) in a time division multiple access (TDMA) broadband fixed wireless access (BFWA) system. At high data rates the intersymbol interference (ISI) induced by dispersive channels becomes a technological bottleneck. Space-time processing at the BS offers a solution to improve the wireless link quality in the uplink. First, we investigate the performance of a space-time decision feedback equalizer (DFE) trained with the LMS algorithm for a single user BFWA system (i.e. one user per frequency channel and per time slot). Then we propose an algorithm for space division multiple access (SDMA) in the uplink based on a combination of adaptive space-time equalization and successive interference cancellation (SIC). It is shown via simulations that this combined approach offers an improvement in the probability of symbol error (P/sub s/) for a two-user system (i.e. two users per frequency channel and per time slot) compared to a space-time DFE without SIC. The RLS algorithm is used for the two-user system to ensure fast convergence. The proposed iterative approach offers a low complexity solution compared to minimum mean square error solutions based on direct matrix inversion, which would be costly for the expected delay spreads associated with BFWA systems.

We consider a mobile network consisting of both the wireless access network and the backhaul network. All base stations in the access network and gateways in the backhaul network are equipped with caches, so that routing costs for serving content requests can be reduced by caching the requested content items closer to the users. In this case, user association in the wireless access network must be aware of both the quality of wireless channels and the content caching strategy. In this paper, we propose a framework that jointly optimizes wireless user association and content caching in both access and backhaul networks. The resulting problem is NP-hard. We propose a polynomial-time algorithm based on convex approximation and pipage rounding that produces a solution within a constant factor of 1 − 1/e from the optimal. Simulation results show that the proposed joint algorithm outperforms schemes that combine cache-independent user association methods with traditional caching strategies (e.g. LRU) in terms of minimizing the aggregate routing cost and backhaul traffic while achieving a high data sum rate in the access network.

Spatial Division Multiplexing (SDM) technology exploits information transmission in spatial dimension in addition to temporal dimension to improve frequency utilization and enlarge transmission capacity. Dynamic adjustment of antenna direction according to the position of targeted user station can better release the potential of SDM. In this paper, we set up a software platform to study the performance of SDM downlink in Radio Access Network (RAN) with dynamic adjustment of antenna direction. Architecture of RAN with TDM/SDM downlink is first introduced to show their difference in slot allocation and transmission capacity. Independent and identically distributed Poisson process is used to simulate the traffic source of downlink. Throughput, packet loss rate and user data rate are calculated for scenarios with TDM and 1 to 4 SDM downlink carriers. Simulation results and analysis indicate that capacity of SDM downlink is of near linear relationship with the number of antennas and transmitters used in central station. Performance of RAN is prospected to be improved enormously by application of SDM technology.

Multiple access methods in a wireless network allow multiple nodes to share a set of available channels for data transmission. The nodes can either compete or cooperate with each other to access the channel(s) so that either an individual or a group objective can be achieved. Game theory, which is a mathematical tool developed to understand the interaction among rational entities, can be applied to model and to analyze individual or group behaviour of nodes for multiple access in wireless networks. Game theory also enables us to model the selfish/malicious behaviour of nodes, and subsequently design the punishment or defense mechanisms for robust multiple access in wireless networks. In addition, game models can provide distributed solutions to the multiple access problems, which are based on solid theoretical foundations. In this survey, we provide a comprehensive review of the game models (e.g., noncooperative/cooperative, static/dynamic, and complete/incomplete information) developed for different multiple access schemes (i.e., contention-free and contention-based random channel access) in wireless networks. We consider time-division multiple access (TDMA), frequency-division multiple access (FDMA), and code-division multiple access (CDMA), ALOHA, and carrier sense multiple access (CSMA)-based wireless networks. In addition, game models for multiple access in dynamic spectrum access-based cognitive radio networks are reviewed. The major findings from the game models used for these different access schemes are highlighted. To this end, several of the key open research directions are outlined.

A cellular communication system is divided into two main parts, core network, and radio access network. This research is concerned with the radio access network part which consists of multiple-cells, each served by a central located base station. Furthermore, the users in each cell are considered to be uniformly distributed inside the cell. In the downlink context, the users’ packets usually arrive at the base station via fiber optic and then are relayed to the users via radio waves of certain frequency/ies. The speeds of delivering users’ packets vary, depending on the users’ location. In this paper, the actual distribution of the service time over different users whose locations are uniformly distributed in a cell served by one base station is analytically found. Simulation results are presented to validate the derived model.

Inspired by the literature on side-channel attacks against cryptographic implementations, we describe a framework for the analysis of location privacy. It allows us to revisit (continuous) re-identification attacks with a combination of information theoretic and security metrics. Our results highlight conceptual differences between re-identification attacks exploiting leakages that are internal or external to a pseudonymised database. They put forward the amount of data to collect in order to estimate a predictive model as an important – yet less discussed – dimension of privacy assessments. They finally leverage recent results on the security evaluations/certification of cryptographic implementations to connect information theoretic and security metrics, and to formally bound the risk of re-identification with external leakages.

It has been demonstrated that turbo codes substantially outperform other codes, e.g., convolutional codes, both in the non-fading additive white Gaussian noise (AWGN) channel as well as multiple-transmit and multiple-receive antenna fading channels. Moreover, it has also been reported that turbo codes perform very well in fast fading channels, but perform somewhat poorly on slow and block fading channels of which the broadband fixed wireless access (FWA) channel is an example. In this paper, we thoroughly compare the performance of turbo-coded and convolutional-coded broadband FWA systems both with and without antenna diversity under the condition of identical complexity for a variety of decoding algorithms. In particular, we derive mathematical expressions to characterize the complexity of turbo decoding based on state-of-the-art Log-MAP and Max-Log-MAP algorithms as well as convolutional decoding based on the Viterbi algorithm in terms of the number of equivalent addition operations. Simulation results show that turbo codes do not offer any performance advantage over convolutional codes in FWA systems without antenna diversity or FWA systems with limited antenna diversity. Indeed, turbo codes only outperform convolutional codes in FWA systems having significant antenna diversity.

Over the past decade, wireless communications has experienced tremendous growth, and this growth is likely to multiply in the near future. The proliferation of mobile users and an ever increasing demand for multimedia services has resulted in greater capacity requirements. Radio frequency spectrum is scarce and cannot meet this ever increasing demand and the required Quality of Service (QoS) will no longer be achieved if efficient Radio Resource Management (RRM) solutions are not found. Conventional Radio Access Networks (RAN) have standalone Base Stations (BS) with capacity preconfigured for peak loads. These RANs have high call blocking and dropping rates since BSs resources cannot be shared. Cloud based RANs (C-RAN) have been proposed as a cost and energy efficient way of meeting high capacity demand of future wireless access networks by consolidating BSs to the cloud. Instead of relying on rejection of new call requests due to limited BS resources, C-RAN takes benefit of the cloud elasticity, which allows dynamic provisioning of cloud BS resources. This paper presents a novel C-RAN Call Admission Control (C-RAN CAC) to ensure Grade of Service (GoS) by improving blocking probability and improvement of call waiting times. Call blocking probability, call average waiting time and system utilization are used to evaluate the performance of the proposed CAC algorithm.

The radio access network (RAN) cooperative caching, which explores the scale effect through cooperative content sharing and caching among multiple RAN caches, is considered as one effective way to fully benefit from the RAN cache. In this paper, we study the feasibility and self-organizing algorithm for RAN cooperative caching. Specifically, we first analyze the real-world dataset of daily content requests from 10 LTE Base Stations (BSs), and find that pursuing high hit rate does not guarantee the reduction of backhaul traffic. Besides, it is shown that content requests from different BSs feature strongly temporal and spatial correlations. To the best of our knowledge, this finding proves the feasibility of RAN cooperative caching for the first time. Then, based on our findings, we propose the self-organizing algorithm for RAN caches to individually decide on how to update their cached content objects, utilizing the defined utility with consideration of the link states among RAN caches, and the size and the request number of the missed and cached content objects. Finally, the performance of our proposed algorithm is validated based on real-world dataset. The results show that the proposed algorithm achieves significant improvement in reducing backhaul traffic. For instance, when cache capacity of each BS is 65% of the traffic generated by non-repeated content objects which are requested in one day over its coverage, the proposed algorithm with 8 defined cooperative caches (CoCas) reaches an average reduction of more than 60% of the backhaul traffic generated in one day over the BS's coverage.

Broadband fixed wireless access (BFWA) systems with multi-hop mesh topologies operating at millimeter-wave bands have attracted considerable attention as a promising technology for high capacity access infrastructures. The primary advantage of the mesh network is an improvement of capacity by means of traffic engineering throughout the network. This work discusses an adaptive load balancing method that enables us to maximize the capacity for the mesh BFWA networks by transferring traffic using multiple routes. Considering wireless link qualities, the adaptive traffic load balancing method attempts to equalize each wireless link's utilization. The proposed method implements flow-based traffic load balancing in order to avoid deteriorating the performance of TCP communications. The performance of the proposed adaptive traffic load balancing method is evaluated on experimental mesh network environments.

One of the major challenges of the telecommunication community for the coming years will be to make multimedia services available to everyone, even to those who are in remote places. Broadband fixed wireless access (BFWA) is one of the best positioned radio access technologies to provide broadband access with performances that surpass current 3G mobile data rates and are similar to wired xDSL systems. The paper addresses the solutions which are proposed and demonstrated in the frame of the IST-STRIKE project to enhance spectral efficiency for BFWA and to guarantee end-to-end quality of service (QoS) through a dual mode HiperMAN/HiperLAN system. The first aspect is covered by the use of multi-transmit multi-receive (MTMR) techniques. Indeed, as it is foreseen that the data rates available with the studied standards will be sufficient for the majority of single user needs, the best way to increase the capacity and lower the deployment cost is to multiply the number of simultaneous transmissions. Besides, it is shown that to ensure QoS for high data rate and time constrained services (such as video streaming), interworking is provided at the data link control (DLC) level.

Broadband fixed wireless access (BFWA) systems operating above 17-GHz band are suitable for high-density deployment of high capacity wireless access infrastructure, while the radio link quality can suffer from rain attenuation especially in rainy climatic regions. In order to overcome the problem and enhance not only the reliability but also the total capacity of the system, the authors have proposed a multi-hop BFWA system with mesh topology. Its unique characteristics include the modulator/demodulator (MODEM) that can adaptively support QPSK, 16 QAM, 64 QAM, 256 QAM and 1024 QAM operation. It has the maximum transmission capacity of 52 Mbits/s per channel at 6.75 MHz symbol rate and attains 364 Mbits/s by multi-channel configuration over the entire 60-MHz bandwidth at 26-GHz band. This paper presents design and implementation of the MODEM together with various data including bit error curves that demonstrate the validity of the design and implementation. A one-year field experiment commenced in April 2004.