Martin Weckerle

Multihop communications in future mobile radio networks

Cellular networks and wireless local area networks (WLAN) are being widely deployed for mobile radio communications. Taking into account the advantageous and drawbacks of both network architectures, it becomes obvious that a combination of them is the logical consequence for future mobile radio networks. The scope of this paper is to introduce a future radio network architecture called hierarchical multihop cellular network (HMCN), which includes several multihop cells. The overlaying cellular network coordinates multihop cells in order to reach an optimal load balance in the whole network. The next evolutionary step towards a HMCN structure is to introduce multihop capable nodes (MHN), which can be fixed or even mobile. The paper shows the challenges and benefits of multihop with fixed nodes, especially the placement of fixed MHN and reduction of radio protocol overhead in order to provide high performance. When MHN are normal mobile nodes, multihop routing becomes a key point in the HMCN concept. The paper proposes a cellular based routing scheme and compares it with the ad hoc routing algorithms being developed by IETF.

Optimal transmitter and jamming strategies in Gaussian MIMO channels

In multiple antenna systems, the impact of concurrent systems depends on the spatial signature of the noise plus interference. We model a two player game in which the user and the jammer have independently fading MIMO channels with different types of channel state information. The objective function is the average performance measured as the trace of an arbitrary matrix-monotone function. For no and perfect CSI, we characterize the saddle-point. For statistical channel information, the optimal transmit strategies are characterized.

Adaptive transmission mode selection scheme for distributed wireless communication systems

The open architecture of distributed wireless communication systems (DWCS) provides the potential to increase capacity. In this letter, we develop an adaptive transmission mode selection (ATMS) scheme for the DWCSs, where the mobile stations (MS) could follow a separate serving, diversity, or data splitting transmission mode, based on the received signal to noise ratio (SNR) from each access point and the required quality-of-service (QoS) of the MSs. The proposed ATMS scheme increases the efficiency and the flexibility of radio resource management for the DWCSs.

Joint channel estimation and symbol detection for SFBC-OFDM systems via the EM algorithm

Joint channel estimation and symbol detection for space-frequency block coded OFDM (SFBC-OFDM) systems is considered. The expectation-maximization (EM) algorithm is employed to devise both soft-in-hard-out (SIHO) maximum likelihood (ML) iterative receivers and soft-in-soft-out (SISO) maximum a posteriori (MAP) iterative receivers for SFBC-OFDM systems. Besides the low computational complexity and fast convergence, the EM-based iterative receivers also have the ability of tracing the variation of fast fading channels, and thus provide quite satisfying performance and bandwidth efficiency even in high-vehicular-speed environment. Numerical results are provided to corroborate the theoretical designs.

Optimum channel estimation over frequency-selective fading channel in multiple antenna systems

In this paper, we derive the optimum channel estimation algorithm based on least square (LS) criterion over frequency-selective fading channel in multiple antenna systems. We prove that in order to minimize the mean square error (MSE) of channel estimation over frequency-selective fading channel, the training sequences for the multiple transmit antennas should be ideally cyclically orthogonal in self-correlation and have zero cross-correlation.

An efficient digital implementation of multicarrier CDMA system based on generalized DFT filter Banks

In this paper, an efficient digital implementation of multicarrier transmission scheme based on generalized discrete Fourier transform (DFT) filter banks is presented for multicarrier code-division multiple-access (MC-CDMA) systems. Generalized DFT filter banks has been traditionally discussed for very high-speed digital subscriber lines (VDSL) wireline systems, received interest also for wireless applications. The design of the generalized DFT modulated filter banks is investigated and its fast implementation is derived in the time-domain for arbitrary integer sampling rate. Through the utilization of the generalized DFT modulated filter banks, one or more subcarriers, even noncontiguous subcarriers can be easily supported by system in both uplink and downlink, which facilitates the users to access the network in a frequency-division multiple-access manner. Simulation results show that the overall bit-error-rate performance of the proposed multicarrier transmission scheme well approaches that of a single-carrier system due to the negligible intercarrier interference introduced by an appropriate design of the generalized DFT modulated filter banks.

Radio resource management in cellular multihop networks

In future mobile broadband radio systems, multihop for coverage extension is seen as a basic building block. Here, we investigate radio resource management (RRM) for multihop networks and assume that the central access point (AP) can control the whole multihop network based on channel state information (CSI) of all links. Specifically we investigate interference effects between neighboring multihop networks as well as within a single multihop network. Interference within a multihop network occurs only when the central scheduler allows simultaneous transmission at the same time and frequency, here called SIMU, on several radio links. It is shown, that SIMU can increase overall capacity of a multihop network compared to a fully orthogonal transmission, here called time division multiple access (TDMA), where only one single link is active at a time. For neighboring multihop networks it is shown that inter cell interference (ICI) may be treated as additive white Gaussian noise (AWGN) with typically only small performance degradation.

Asynchronous uplink transmission in FMT-FDMA systems

Multi-carrier (MC) transmission is seen as the leading candidate for beyond 3G mobile communications. We focus here on the MC scheme known as filtered multi tone (FMT) modulation. We investigate its suitability for an asynchronous uplink multi-user scenario, under the hypothesis of frequency division multiple access (FDMA). In particular, we show the influence of the filter spectral characteristics and the effects of introducing some redundancy in bandwidth through non-critical sampling. Furthermore, we compare the achievable performance with that of an OFDMA system over an AWGN channel in terms of bit error rate.

Space-time joint channel estimation in filtered multitone based multicarrier multibranch systems

In this paper, we investigate some space-time joint channel estimation (JCE) schemes in filtered multitone (FMT) based multicarrier multibranch (multiuser and/or multiantenna) systems. Each subcarrier is proposed to be processed separately due to the spectral characteristics of the FMT signals On each subcarrier, the wireless channels experienced by all transmit branches are estimated jointly at the receiver. The least square (LS) space-time JCE and weighted least square (WLS) schemes are derived. The constant amplitude zero auto-correlation (CAZAC) code based pilots are proposed for the aforementioned multicarrier applications to reduce the mean square estimation error. Simulation results are provided to validate the theoretical analysis.

Dynamic classmarks for SDR equipment

The paper describes a dynamic classmark scheme based on a finite number of stages during a radio connection procedure for reconfigurable terminals in future multiple radio access technology environments. Based on the user profile, terminal profile and service profile that the user applies, features are clustered into different sets called classmarks. The classmarks are designed in a stage-based manner in order to realize the method of dynamically creating and triggering them. During the reconfiguration, radio link establishment and communication processes, the number of stages is adaptive to the access frequency and priorities of the necessary features required by the network. Thanks to this approach, the signaling burden is highly reduced in the radio network. Therefore, the efficiency of radio resource management is improved.