Ralf Pabst

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.

Performance evaluation of a fixed relay concept for next generation wireless systems

This work presents a concept and the related performance evaluation for a wireless broadband system based on fixed relay stations acting as wireless bridges. The system is intended for dense populated areas as an overlay to cellular radio systems. A short introduction is given to the general topic of fixed relaying, the proposed extension to a MAC-frame based access protocol like IEEE 802.11e, 802.15.3, 802.16a and HIPERLAN2 is outlined. A possible deployment scenario is introduced and the simulative traffic performance in a Manhattan-like dense urban environment is presented. It is established that the fixed relaying concept is well suited to substantially contribute to provide high capacity cellular broadband radio coverage in future (NG) cellular wireless broadband systems.

Fixed Relays for Next Generation Wireless Systems

This chapter presents a concept and the related performance evaluation for a wireless broadband system based on fixed relay stations acting as wireless bridges. The system is equally well-suited for both dense populated areas and wide-area coverage as an overlay to cellular radio systems. A short introduction is given to the general topic of fixed relaying. The proposed extension to a Medium Access Control-frame based access protocol like IEEE802.11e, 802.15.3, 802.16a and HIPERLAN2 is outlined. A possible deployment scenario is introduced and the simulative traffic performance in a Manhattan-like dense urban environment and a wide-area open-space environment is presented. It is established that the fixed relaying concept is well suited to substantially contribute to provide high capacity cellular broadband radio coverage in future (NG) cellular wireless broadband systems.

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.

System Level Performance of Cellular WiMAX IEEE 802.16 with SDMA-enhanced Medium Access

Recent years have witnessed an ever-increasing interest in smart antenna technologies to boost the capacity of existing and future wireless systems. As one of the first standards the wireless metropolitan area network IEEE 802.16 (WiMAX) provides means to support these techniques. This paper investigates the potential of smart antenna beamforming and space division multiple access (SDMA) in the context of a cellular IEEE 802.16 deployment. It presents the system level performance evaluation of a joint TDMA/SDMA scheduling approach taking into account the influence of intra- and inter-cell interference generated by concurrent SDMA transmissions. The performance of single- and multi-user beamforming is compared with the non-beamforming reference case.

Evaluation of Grouping Strategies for an Hierarchical SDMA/TDMA Scheduling Process

Adding SDMA capabilities to modern wireless communication systems like IEEE 802.16 WiMAX promises high system capacity gains but raises the problem of combining orthogonal medium access schemes like TDMA with the non- orthogonal SDMA. In order to reduce the complexity and to improve the flexibility of a joint SDMA/TDMA scheduler, the scheduling process can be subdivided into two parts. First, a spatial grouping algorithm forms groups of users that can be co-scheduled because of their spatial separability. Then, a group scheduling algorithm allocates resources of the time domain to the spatial groups. This paper focuses on the first part of the hierarchical SDMA/TDMA scheduling process, i.e., the spatial grouping. It outlines different grouping strategies and it analyzes their computational complexity. Their respective grouping performance is evaluated according to a metric introduced in the paper. Finally, a tree-based grouping strategy is recommended based on its low complexity and good performance.

Multimode communication protocols enabling reconfigurable radios

This paper focuses on the realization and application of a generic protocol stack for reconfigurable wireless communication systems. This focus extends the field of software-defined radios which usually concentrates on the physical layer. The generic protocol stack comprises common protocol functionality and behavior which are extended through specific parts of the targeted radio access technology. This paper considers parameterizable modules of basic protocol functions residing in the data link layer of the ISO/OSI model. System-specific functionality of the protocol software is realized through adequate parameterization and composition of the generic modules. The generic protocol stack allows an efficient realization of reconfigurable protocol software and enables a completely reconfigurable wireless communication system. It is a first step from side-by-side realized, preinstalled modes in a terminal towards a dynamic reconfigurable anymode terminal. The presented modules of the generic protocol stack can also be regarded as a toolbox for the accelerated and cost-efficient development of future communication protocols.

Efficient multimode protocol architecture for complementary radio interfaces in relay-based 4G networks

Wireless networks of the next generation will satisfy user demand for a ubiquitous mobile broadband access. Current research efforts are therefore targeting the efficient realization of a flexible radio interface and network architecture. The wide range of application scenarios seems to prohibit a “one radio interface fits all” solution. Instead, it requires a multitude of solutions tailored for specific communication environments. Ideally, these solutions are related radio interface modes that have a common technology basis. This article presents a protocol reference architecture that enables the efficient integration of multiple such modes in a complementary way. This architecture essentially benefits from the commonalities between these modes. Hence it facilitates the coexistence and cooperation of different modes in all devices of a future relaybased radio access network: user terminals, access points, and relay nodes. This article focuses on the realization of the multimode capability of user and control planes and the related management of the protocols of a flexible radio interface. A proof of concept and its evaluation are presented at the example of relay-based 4G broadband networks and IEEE 802.16 (WiMAX).

Fixed relays for next generation wireless systems — System concept and performance evaluation

This work presents a concept and the related analysis of the traffic performance for a wireless broadband system based on fixed relay stations acting as wireless bridges. The analysis focuses on the important performance indicators end-to-end throughput and delay, taking into account the effects of an automated repeat request protocol. An extension to a MAC frame based access protocol like IEEE 802.11e, 802.15.3, 802.16a, and HIPERLAN2 is outlined and taken as basis for the calculations. The system is intended for both dense populated areas as an overlay to cellular radio systems and to provide wide-area broadband coverage. The two possible deployment scenarios for both dense urban and wide-area environments are introduced. Analytical and validating simulation results are shown, proving the suitability of the proposed concept for both of the mentioned scenarios. It is established that the fixed relaying concept is well suited to substantially contribute to provide high capacity cellular broadband radio coverage in next generation (NG) cellular wireless broadband systems.