Daniel C. Schultz

Relay-based deployment concepts for wireless and mobile broadband radio

In recent years, there has been an upsurge of interest in multihop-augmented infrastructure-based networks in both the industry and academia, such as the seed concept in 3GPP, mesh networks in IEEE 802.16, and converge extension of HiperLAN/2 through relays or user-cooperative diversity mesh networks. This article, a synopsis of numerous contributions to the working group 4 of the wireless world research forum and other research work, presents an overview of important topics and applications in the context of relaying. It covers different approaches to exploiting the benefits of multihop communications via relays, such as solutions for radio range extension in mobile and wireless broadband cellular networks (trading range for capacity), and solutions to combat shadowing at high radio frequencies. Furthermore, relaying is presented as a means to reduce infrastructure deployment costs. It is also shown that through the exploitation of spatial diversity, multihop relaying can enhance capacity in cellular networks. We wish to emphasize that while this article focuses on fixed relays, many of the concepts presented can also be applied to systems with moving relays.

Capacity of a relaying infrastructure for broadband radio coverage of urban areas

Owing to the difficult propagation conditions in the frequency range of future cellular broadband radio systems, very small cell sizes and high attenuation through obstacles (sufficient C/I ratio only in direct line of sight (LoS)) are expected to constitute a major challenge for the development of such systems. Thus, complete coverage of urban areas using a conventional (one-hop) cellular infrastructure is expected to be very costly due to the high number of base stations and fixed network connections needed. For this reason, the introduction of relaying is widely accepted to be an essential element in the development of future cellular broadband radio networks. This paper presents a methodology to quantify the influence of relaying on the capacity of a single base station. We define the capacity as the aggregate downlink throughput that is achieved by all users in the cell. Inspired by the recently proposed wireless media system (WMS) architecture [B. Walke, et al., Apr. 2003], we compare the capacity of a conventional one-hop cellular architecture with the capacity of a configuration consisting of one base station and four regenerative fixed relay stations (FRS) that together cover the same area like five base stations in a conventional cellular architecture. The presented methodology allows exploring the parameter space, which is spanned by system parameters like antenna gain, scenario geometry, and noise and transmitting power.

A mobile broadband system based on fixed wireless routers

A new radio access network architecture for a mobile broadband system is introduced that uses fixed wireless routers to provide radio coverage to otherwise shadowed areas. Highest spectrum capacity and lowest possible transmit power as main targets will be reached by using low power (1 W) pico base stations using a wireless or mobile broadband air interface at access points (AP) to the core network and at FWRs to trade the high capacity available at APs against radio coverage range. The so-called wireless media system (WMS) will provide broadband access to terminals with medium velocity of movement and is embedded into a cellular radio network to support a high velocity of terminals with medium transmission rate. The low power used at the base stations leads to a pico-cellular concept relying essentially on multi-hop communication across fixed wireless bridges or routers and to some extent also on ad hoc networking. The new concept to achieve broadband radio coverage in densely populated areas is described and first analysis results of some crucial elements are presented.

Fixed Relays for Cost Efficient 4G Network Deployments: An Evaluation

The paper provides a qualitative performance assessment of relay based deployment concepts in comparison to single-hop deployment. The results in this paper prove the general assumption that the deployment of relay nodes (RNs) provide a strong opportunity to reduce the network deployment cost substantially. It is shown how low power RNs have to be applied in cellular scenarios with high power base stations (BSs) and what cost benefits can be expected. The qualitative results show that the low power relays do have the potential to decrease the deployment cost. It is further shown that a parallelization of the relay link between the RNs and the serving BS will help to improve the cost efficiency of the relay based deployment concept.

Layer-2 Relays in Cellular Mobile Radio Networks

This paper discusses fixed layer-2 relays for infrastructure based radio network deployment concepts. Relay enhanced cells (RECs) for different optimizations goals like area size optimization, cell capacity optimizations in a given area and the application of relays to cover otherwise shadowed areas are introduced. As a basis for the proof of concept by means of simulation, a relaying capable MAC protocol as well as the used REC concept is briefly explained. The new REC concepts for both, area optimizations and capacity optimizations are validated by analytic and simulation results. The results are shown for the C/I in a multi-cellular environment and the throughput for an REC cluster with four relay nodes per REC using different cluster orders. The results are compared to that of a comparable single-hop cell cluster

Performance Evaluation of a Relay-Based 4G Network Deployment with Combined SDMA/OFDMA and Resource Partitioning

This work presents a low-cost, low complexity deployment concept for a relay-based cellular broadband network. The concept is based on a combination of a multi-antenna OFDMA base station (BS) and simple, single-antenna OFDMA relay nodes (RN) and user terminals (UT). The concept further encompasses a partitioning of the available radio resources in the frequency domain to control interference within and between relay enhanced cells (REC). The performance of the proposed system in a suburban cellular setup is evaluated by means of stochastic, event-driven simulation and a comparison against a pure BS-only scenario is made.

Analytical Estimation of Packet Delays in Relay-Based IMT-Advanced Networks

The paper shows that relays as inherent technology of IMT-advanced system can provide low delays as required for future multimedia services. The results shown prove that the proposed relaying scheme is able to keep relay requirements on the air interface and to support delay sensitive high interactive services. The analytical results are validated by system level simulations, which show that the relay might become even more important for real scenarios in order to connect the user terminal (UT) on the uplink.

Combined Uplink Resource Reservation and Power Control for Relay-Based OFDMA Systems

This work presents a combined Uplink Resource Reservation and Power Control framework for Relay-Based OFDMA systems, i.e. for typical IMT-Advanced candidate systems. The framework serves to provide both fair uplink scheduling and a balanced link budget in a relay deployment. The performance of the proposed framework in a suburban cellular setup is evaluated by means of stochastic, event-driven simulation.

Performance evaluation for IEEE 802.11G hot spot coverage using sectorised antennas

Wireless local area networks (WLANs) have a tremendous success in today short range communication. The user density is permanently increasing and the planning focus shifts from pure coverage issues towards capacity improvements. As IEEE 802.11 was originally planned for ragged coverage, cell planning issues have been neglected. Especially for hot spots they now become important. In this paper, we show the supply of an exhibition hall with IEEE 802.11 service using sectorised antennas. A capacity increase by a factor 2 compared to omnidirectional antennas shows that this proven technology also works in the decentralised area. Special problems of the IEEE 802.11 system are investigated by a performance evaluation using stochastical simulations.

Analysis of Performance of a TDMA-based Distributed MAC Protocol in Single-hop Wireless Networks

Nowadays, the IEEE 802.11 infrastructure basic service set (BSS) network is the most widely used wireless LAN (WLAN) system. There are growing needs to interconnect access points (APs) of separate BSSs to create an IEEE 802.11 extended service set (ESS) mesh network over the wireless medium. Mesh distributed coordination function (MDCF) is a novel medium access control (MAC) protocol, designed for interconnecting a large number of APs to form an efficient wireless multi-hop network supporting quality of service (QoS). Based on that an efficient ESS mesh network can be created. This paper evaluates the traffic performance of MDCF by using the analytical approach. Based on the established mathematical model, the optimal frame parameter settings for MDCF can be precisely determined.