Friedbert Berens

Joint detection for multicarrier CDMA mobile radio systems. I. System model

The combination of code division multiple access (CDMA) and multicarrier (MC) transmission techniques, termed MC-CDMA, is considered an interesting alternative to conventional DS (direct sequence)-CDMA. Therefore, recent research activities have focused on the application of MC-CDMA in mobile radio systems. The presently investigated MC-CDMA concepts explicitly avoid the occurrence of intersymbol interference (ISI), which facilitates the use of simple receivers. Unfortunately, the application of such MC-CDMA concepts cannot be recommended in outdoor environments, which are characterized by high speed mobiles and considerable excess delays of the mobile radio channel. An MC-CDMA concept, which overcomes this disadvantage, is proposed and described mathematically for the first time.

Channel decoder architecture for 3G mobile wireless terminals

Channel coding is a key element of any digital wireless communication system since it minimizes the effects of noise and interference on the transmitted signal. In third-generation (3G) wireless systems channel coding techniques must serve both voice and data users whose requirements considerably vary. Thus the third generation partnership project (3GPP) standard offers two coding techniques, convolutional-coding for voice and turbo-coding for data services. In this paper we present a combined channel decoding architecture for 3G terminal applications. It outperforms a solution based on two separate decoders due to an efficient reuse of computational hardware and memory resources for both decoders. Moreover it supports blind transport format detection. Special emphasis is put on low energy consumption.

A synthesizable IP core for WiMedia 1.5 UWB LDPC code decoding

The upcoming WiMedia 1.5 standard for Ultra-Wideband (UWB) supports payload throughputs of more than 1 Gbit/s. It features Low-Density Parity Check (LDPC) codes as coding scheme for the high data rate modes. LDPC decoder design for this standard is a very challenging task, since it has to offer high throughputs, low latency, excellent error correction capabilities, and furthermore flexibility.

Joint detection for multicarrier CDMA mobile radio systems. II. Detection techniques

For pt.I see ibid., p.991, 1996. Presently investigated multicarrier code division multiple access (MC-CDMA) concepts explicitly avoid the occurrence of intersymbol interference (ISI), which facilitates the use of simple receivers. Unfortunately, the application of such MC-CDMA concepts cannot be recommended in outdoor environments. In pt. I, an MC-CDMA concept, which overcomes this disadvantage, has been introduced and described mathematically for the first time. The presented MC-CDMA concept explicitly allows ISI. In order to mitigate the effects of multiple access interference (MAI) and ISI, the deployment of joint detection (JD) techniques is proposed. Four JD techniques which are suitable for the application in the presented MC-CDMA concept are introduced. Finally, the performance, which can be achieved by applying the proposed JD techniques in the presented MC-CDMA concept, is analyzed in the case of the uplink.

The European flexible DAA approach towards an open UWB regulation

After an initial regulatory framework for Ultra Wide Band (UWB) devices in Europe has been established in 2006 [3] by the CEPT additional work started in order to extend the usable band for UWB devices in Europe using active and passive mitigation techniques. In an initial step the passive Low Duty Cycle (LDC) mitigation techniques has been introduced in the band 3.4 GHz to 4.8 GHz in December 2006 [6] covering UWB devices for positioning and low data rate communication applications. In order to be able to accommodate high data rate UWB devices in the band 3.1 GHz to 4.8 GHz and the band 8.5 GHz to 9.0 GHz active mitigation techniques based on Detect and Avoid (DAA) are required to protect the potential victim services like radio navigation services and broadband wireless access services, in these bands. Based on this requirement the CEPT TG3 group on UBW regulation in Europe has defined a new flexible DAA mitigation technique for UWB devices operating in the bands 3.1 GHz to 4.8 GHz and 8.5 GHz and 9.0 GHz. The resulting regulation will be published end of 2008 as official ECC decision on UWB devices using DAA [7]. In the scope of ETSI ERM TG3 la and the Special Taskforce on DAA UBW devices (STF- 250) the work on a harmonized standard has started recently [8].

A Survey on LDPC Codes and Decoders for OFDM-based UWB Systems

Current UWB systems apply convolutional codes as their channel coding scheme. For next generation systems LDPC codes are in discussion due to their outstanding communications performance. LDPC codes are already utilized in the new WiMax and WiFi standards. Thus it is reasonable to investigate these codes as candidate LDPC codes for UWB. In this paper the authors present an implementation complexity and performance comparison of LDPC decoders. We will show that it is of great advantage to design new LDPC codes which are tailored to the special latency and throughput constraints of upcoming UWB systems. This new class of LDPC codes is named ultra-sparse LDPC codes. Synthesis results of WiMax, WiFi, and U-S LDPC decoders are presented based on an enhanced 65 nm CMOS process. We show that the implementation complexity of the new U-S LDPC decoders is 55% smaller, utilizing only 0.2 mm2 instead of over 0.4 mm2, while the communications performance of all observed LDPC codes are almost identical under all the considered UWB simulation conditions.

Implementation aspects of turbo-decoders for future radio applications

Turbo codes will most likely be employed in future radio systems as a channel coding scheme for high-rate data services. However, turbo decoding is a comparatively complex task. To obtain efficient decoder implementations, the system design space has to be explored on multiple levels. In this paper, we span the system design space for turbo codes and describe a method of exploration, while focusing on the implementation-dependent part. The design decisions taken during exploration are rated regarding complexity, throughput and power consumption. The second part of our paper evaluates sample software and hardware implementations of a 2 Mbit/s turbo decoder.

Enhanced Channel Coding for OFDM-based UWB Systems

In this paper the authors present an enhanced channel coding scheme and architecture providing LDPC codes for the use in future generations of the WIMEDIA UWB industry standard. Main emphasis is put on the development of a low complex LDPC code which provides a throughput of at least 1.1 Gbit/s, with a reduced number of iterations even up to 1.6 Gbit/s. By using such an enhanced channel coding scheme the range or the data rate of the WIMEDIA UWB system could be remarkably increased with a limited increase in implementation complexity with respect to silicon area

Performance of multicarrier joint detection CDMA mobile communications systems

For future mobile communications, an appropriately chosen multiple access scheme is a critical issue. To support robust frequency planning, multi-operator scenarios, system coexistence and hierarchical cell structures, frequency division multiple access (FDMA) and multicarrier techniques are viable choices. Further multiple access schemes presently under discussion are code division multiple access (CDMA) and time division multiple access (TDMA). A mobile radio system concept deploying a hybrid frequency and time divided code division multiple access (F/T/CDMA) scheme with a multicarrier CDMA (MC-CDMA) component, called MC/JD-CDMA, is proposed and performance results for the uplink are presented. Attractive features of the proposed system concept are the possibility to flexibly offer voice and data services with different bit rates, soft capacity, as well as inherent frequency and interferer diversity.

On multicarrier CDMA mobile radio systems with joint detection and coherent receiver antenna diversity

The combination of code division multiple access (CDMA) and multicarrier (MC) transmission techniques, termed MC-CDMA, is considered a promising alternative to conventional DS (direct sequence)-CDMA. An MC-CDMA concept which is well-suited for mobile radio applications is described. This concept overcomes the disadvantages of previously proposed concepts. In MC-CDMA mobile radio systems, signal reception is impaired by time-varying multipath propagation. The impairments can be reduced by coherent receiver antenna diversity (CRAD). The application of CRAD in combination with joint detection (JD) techniques to the more critical uplink of MC-CDMA mobile radio systems is investigated. Four JD techniques for CRAD are presented and their performance are studied.