Markus Muck

A pseudorandom postfix OFDM modulator - semi-blind channel estimation and equalization

This paper details a new orthogonal-frequency-division-multiplexing (OFDM) modulator based on the use of a pseudorandom postfix (PRP)-OFDM and discusses low-complexity equalization and channel estimation/tracking architectures. The main property of this new modulation scheme is the ability to estimate and track the channel variations semi-blindly using order-one statistics of the received signal. Compared with known cyclic prefix OFDM (CP-OFDM) pilot-symbol-assisted modulation (PSAM) schemes, the pilot overhead is avoided: The channel estimation is performed based on the exploitation of pseudorandomly weighted postfix sequences replacing the guard interval contents of CP-OFDM. PRP-OFDM is shown to be of advantage if the target application requires 1) a minimum pilot overhead, 2) low-complexity channel tracking (e.g., high mobility context), and 3) adjustable receiver complexity/performance trade-offs (available due to the similarities of PRP-OFDM to the zero-padded OFDM (ZP-OFDM) modulation scheme) without requiring any feedback loop to the transmitter.

A pseudo random postfix OFDM modulator and inherent channel estimation techniques

The paper details a new OFDM modulator based on the use of a pseudo random postfix (PRP-OFDM) and low complexity equalization architectures. The main advantage of this new modulation scheme is the ability to estimate and track channel variations blindly using order one statistics of the received signal. This scheme is thus very well suited in the presence of large Doppler spreads where channel tracking becomes essential. Moreover, the proposal of various equalization structures, derived from the zero padded transmission schemes, allows implementations ranging from low-complexity/medium performance to increased-complexity/high performance.

A MMSE successive interference cancellation scheme for a new adjustable hybrid spread OFDM system

The effects of uniform spreading in OFDM-CDMA systems is the harmonization at the reception of the signal to noise ratio between the sub-bands which prevents the good performance of successive decoding algorithms. This paper proposes a new hybrid spread OFDM (SOFDM) transmission scheme in which the spreading of the information is adjustable and not uniform along the carrier (frequency selective). Moreover a MMSE version of the V-BLAST successive interference cancellation algorithm suited for this hybrid modulator is derived. The performance of the combination of SHOFDM and MMSE V-BLAST is shown to both outperform COFDM and conventional and classical iterative detection algorithms for SOFDM in the realistic scenario of the 5 GHz HiperLAN/2 system.

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

An important emerging capability is for mobile terminals to be dynamically reconfigured. Through ongoing advances in technology such as software defined radio, reconfiguration of mobile terminals will in the near future be achievable across all layers of the protocol stack. However, along with the capability for such wide-ranging reconfiguration comes the need to manage reconfiguration procedures. This is necessary to coordinate reconfigurations, to ensure that there are no negative effects (e.g. interference to other RATs) as a result of reconfigurations, and to leverage maximal potential benefits of reconfiguration and ensuing technologies such as those involving dynamic spectrum access. The IEEE P1900.4 working group is therefore defining three building blocks for reconfiguration management: network reconfiguration management (NRM), terminal reconfiguration management (TRM), and a radio enabler to provide connectivity between the NRM and TRMs. In this paper we concentrate on aspects of the radio enabler, highlighting its relevance in heterogeneous radio access scenarios, its advantages, and some aspects of its technical realization.

IEEE P1900.B: Coexistence Support for Reconfigurable, Heterogeneous Air Interfaces

This contribution presents and discusses the system concept approach which has been proposed by the European Integrated Project IST-E2R II in the IEEE P1900.B Standardization Study Group (SG); it currently is under further elaboration in the framework of the follow-up IEEE P1900.4 Working Group (WG) whose Project Authorization Request (PAR) was accepted in December 2006. This effort targets reconfigurable (typically software defined radio (SDR) based) networks and terminals in a heterogeneous wireless environment, with multi-homing capable terminals enabling the users to operate multiple wireless links simultaneously. In order to ensure backwards compatibility to legacy standards, the approach is to introduce three new building blocks into the (existing and/or evolving) heterogeneous landscape: i) A network reconfiguration management module, ii) a radio enabler and iii) a terminal reconfiguration management module. Within this paper, the key functionalities of these building blocks are detailed and discussed; it is furthermore outlined how the introduction of distributed decision-making concepts improves the efficiency of the heterogeneous system in terms of i) signaling overhead, ii) reactivity of user mobile terminals (MTs) and iii) numerical resource selection optimization complexity on the network side.

Iterative interference suppression for pseudo random postfix OFDM based channel estimation

This contribution proposes an iterative channel impulse response (CIR) estimation scheme in the context of the pseudo-random-postfix OFDM (PRP-OFDM) modulation. While conventional techniques reduce noise and interference of OFDM data symbols on the CUR estimates by simple mean value calculation, the new proposal uses soft decoder outputs in order to perform iterative OFDM data symbol interference cancellation. In a typical example for 64QAM constellations, the mean-square-error (MSE) of the CIR estimates is improved by approx. 12 dB after three iterations. Based on PRP-OFDM postfixes only, it is thus possible to perform channel estimation for higher order constellations (64QAM and higher) with an initial CIR estimation over a small observation window (for 64QAM typically 30 to 40 OFDM symbols). Any loss in throughput due to additional redundancy for CIR estimation purposes, e.g. pilot tones, learning symbols, etc. is avoided at the cost of an increase in decoding complexity.

CPC-assisted Network Selection Strategy

In a beyond 3G context, many wireless technologies can cooperate or interoperate, within dynamic and reconfigurable networks. In this changing radio environment, the challenge for the cognitive terminal is to be able to connect to the relevant network, according to several criteria. E2R has developed concepts and solutions for a Cognitive Pilot Channel (CPC) to bring enough information to the terminals for network selection when terminals are proceeding either initial connection or handoff. This paper focuses on the network selection strategy according to the information which could be brought by CPC and also some information of user preference stored in terminals previously. In the latter part, a network selection algorithm is presented, which can both improve the system performance and satisfy users well.

Distributed discrete resource optimization in heterogeneous networks

Nowadays, the emergence of many radio technologies has increased the research interest towards Radio Resources Management (RRM) in heterogeneous systems. In this context, we seek a distributed scheme for discrete resource allocation. The algorithm proposed should reduce computation and signalling overhead, compared to centralized optimization or distributed solutions based on Game Theory. Therefore, the solution proposed here consists in splitting the resource allocation problem into two parts. First, Users and Base Stations negotiate a mean allocation using a Multisystem Minimum Mean Rate Scheduling (M3RS) algorithm presented here. Then, Base Stations allocate power independantly and instantaneously in order to cope with changing radio conditions. This problem is widely known in literature and is not developped here.

Evolution of Wireless Communication Systems Towards Autonomously Managed, Cognitive Radio Functionalities

This contribution presents key functionalities and design approaches of a distributed system architecture as it is studied in the framework of the European E2R II project. An emphasis is laid on policy based self-governance, distributed reconfiguration concepts and corresponding cognitive support functionalities; this support is necessary to assure context awareness in the equipment in order to facilitate (enable) distributed decision making. The idea is to distribute decision making functionalities among network and user equipment elements in order to (i) limit the required calculation complexity on the network and user side for the determination of the optimum resource selection strategy, (ii) increase the reactivity of the equipment to any context change minimizing the required amount of human interaction and (iii) minimize the signaling overhead by broadcasting generic policy rules applicable to all users instead of targeting a user-by-user based reconfiguration approach. A simple use case illustrates how Game Theoretic tools can be used in order to derive suitable policies and how to perform decisions.

Radio Access Technology Selection enabled by IEEE P1900.4

This paper addresses the implementation of decentralized RAT selection strategies at the mobile terminal in a heterogeneous wireless network scenario. This can be achieved if the network provides some information or guidelines to assist the terminal in its decisions, making use of the IEEE P1900.4 protocol. In order to illustrate the procedure, a specific RAT selection strategy for heterogeneous CDMA/TDMA networks devoted to reduce interference by allocating users according to the measured path loss is analyzed. Results show that the proposed decentralized strategy is able to outperform a reference centralized load-balancing strategy.