Pfm Peter Smulders

Exploiting the 60 GHz band for local wireless multimedia access: prospects and future directions

This article addresses basic issues regarding the design and development of wireless access and wireless LAN systems that will operate in the 60 GHz band as part of the fourth-generation (4G) system. The 60 GHz band is of much interest since this is the band in which a massive amount of spectral space (5 GHz) has been allocated worldwide for dense wireless local communications. The article gives an overview of 60 GHz channel characteristics and puts them in their true perspective. In addition, we discuss how to achieve the exploitation of the abundant bandwidth resource for all kinds of short-range communications. The main tenor is that an overall system architecture should be worked out that provides industry with plenty of scope for product differentiation. This architecture should feature affordability, scalability, modularity, extendibility, and interoperability. In addition, user convenience and easy and efficient network deployment are important prerequisites for market success. This article discusses these features and indicates a number of key research topics.

Channel characteristics and transmission performance for various channel configurations at 60 GHz

Extensive measurements are conducted in room environments at 60 GHz to analyze the channel characteristics for various channel configurations. Channel parameters retrieved from measurements are presented and analyzed based on generic channel models. Particularly, a simple single-cluster model is applied for the parameter retrieval and performance evaluation. By this model, power delay profiles are simply described by a-factor, a root-mean-squared delay spread, and a shape parameter. The considered channels are configured with the combination of omnidirectional, fan-beam, and pencil-beam antennas at transmitter and receiver sides. Both line-of-sight (LOS) and non-LOS (NLOS) channels are considered. Further, to evaluate the transmission performance, we analyze the link budget in the considered environments, then design and simulate an OFDM system with a data rate of 2 Gbps to compare the bit-error-rate (BER) performance by using the measured and modeled channels. Both coded and uncoded OFDM systems are simulated. It is observed that the BER performance agrees well for the measured and modeled channels. In addition, directive configurations can provide sufficient link margins and BER performance for high data rate communications. To increase the coverage and performance in the NLOS area, it is preferable to apply directive antennas.

On the influence of phase noise induced ICI in MIMO OFDM systems

The influence of transmitter and receiver phase noise (PN) on the performance of a multiple-input multiple-output orthogonal frequency division multiplexing (MIMO OFDM) based communication system is analyzed. It is shown that in the case of frequency flat Rayleigh fading, the influence of receiver and transmitter PN is equal. In the case of independent Rayleigh fading, however, the impact of the receiver PN is shown to depend on the ratio between the number of transmit and receive branches.

Estimation and Compensation of Frequency Selective TX/RX IQ Imbalance in MIMO OFDM systems

The influence, digital estimation and compensation of IQ mismatch at both transmitter (TX) and receiver (RX) side of a direct-conversion based multiple antenna OFDM system are presented in this paper. The resulting IQ imbalance can be split into a frequency independent and a frequency selective part. For estimation and compensation a two-step approach is presented, combining a data-aided and decision directed approach. First the frequency independent IQ imbalance is estimated using a preamble and, subsequently, the frequency selective IQ imbalance is removed using adaptive filtering. A numerical performance analysis reveals that the presented approach effectively mitigates the influence of IQ mismatch in OFDM-based space division multiplexing systems experiencing both TX and RX IQ imbalance.

Estimation and compensation of TX and RX IQ imbalance in OFDM-based MIMO systems

This paper studies the influence, estimation and digital compensation of IQ imbalance at both transmitter and receiver side of a multiple-input multiple-output (MIMO) OFDM system. Hereto a preamble is designed, which enables simultaneous estimation of the channel and imbalance parameters. New estimation approaches for TX, RX and joint TX and RX IQ imbalance in MIMO OFDM systems are proposed and evaluated. Results from a numerical study show that all three proposed compensation approaches are able to significantly suppress the influence of IQ mismatch.

Influence and suppression of phase noise in multi-antenna OFDM

The influence of phase noise (PN) on the performance of a multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) based communication system is analyzed. As part of this analysis, an estimator for the common phase error (CPE) is derived, based on the maximum likelihood estimation (MLE), which was chosen for its asymptotic optimality. Since the computational complexity of the MLE procedure clearly rules out a cost effective solution, a reduced-complexity algorithm. based on least squares estimation (LSE) is designed which yields suboptimal performance. Simulation results reveal that the difference in bit-error-rate performance between systems applying the LSE or MLE of the CPE is very small. This implies that the LSE is well applicable for 802.11a based MIMO systems.

Performance analysis of zero-IF MIMO OFDM transceivers with IQ imbalance

This contribution analytically studies the influence of IQ mismatch on the performance of multiple-antenna orthogonal frequency division multiplexing (OFDM) systems based on the zero-IF architecture. First a system model for such a multiple-input multiple-output (MIMO) OFDM system experiencing both transmitter (TX) and receiver (RX) IQ imbalance is derived. This is used to obtain analytical expressions for the probability of error in symbol detection for MIMO OFDM systems in Rayleigh faded multipath channels. The derived results can be used to find matching specifications for the TX- and RX-branches for different multicarrier MIMO systems. It is concluded that in fading channels RX IQ imbalance is on average more destructive than TX IQ imbalance. Additionally, it is concluded that the addition of extra RX antennas is beneficial to reduce the dependence on RX IQ imbalance, but increases at the same time the impact of TX IQ imbalance.

Indoor Channel Measurements and Analysis in the Frequency Bands 2 GHz and 60 GHz

This paper describes the wideband measurements conducted at the frequencies 58 GHz and 2.25 GHz in an indoor environment. Normalized received power (NRP) and root-mean-squared (RMS) delay spread are calculated and used to compare the characteristics of radio wave propagation in both line-of-sight and non-line-of-sight areas at the two frequencies. The results show that on top of the difference in free space, the NRP at 58 GHz is several dBs lower than at 2.25 GHz in average. This difference is also reflected in the fitted log-(virtual) distance NRP models. In the deep shadow region, the poor diffraction level at 58 GHz will reduce the power level, but meanwhile the reflected waves from walls have a strong contribution to the received signal. In addition, it is observed that the radio channel at 58 GHz shows much less time dispersion in terms of RMS delay spread. The results can be quite useful for the 60 GHz system design, which might be very different from the design of conventional systems which operate in the lower frequency bands

Distribution of the ICI Term in Phase Noise Impaired OFDM Systems

Orthogonality between the subcarriers of an orthogonal frequency division multiplexing (OFDM) system is affected by phase noise, which causes inter-carrier interference (ICI). The distribution of this interference term is studied in this paper. The distribution of the ICI for large number of carriers is derived and it is shown that the complex Gaussian approximation, generally applied in previous literature, is not valid and that the ICI term exhibits thicker tails. An analysis of the tail probabilities confirms these finding and shows that bit-error probabilities are severely underestimated when the Gaussian approximation for the ICI term is used, leading to too optimistic design criteria. Results from a simulation study confirm the analytical findings and show the validity of the limit distribution, obtained under the assumption of a large number of subcarriers, already for a modest number of subcarriers.

Impact of antenna pattern and reflective environment on 60 GHz indoor radio channel characteristics

Wideband channel measurements at the 60-GHz frequency band in a reflective environment with different antenna heights are presented. The log-distance model of the normalized received power (NRP) is used to fit the measured data for both line-of-sight (LOS) and nonline-of-sight (NLOS) cases. Also, the impact of the biconical antennas and the reflective environment on the channel properties is analyzed and explained. Results show that the most favorable NRP values are found in the case that the Tx and Rx antennas are at the same height. Also, in most cases, the scatter paths have more contributions on the total received power than the direct path. In addition, in the LOS case, the NRPs become less dependent on the Tx-Rx separation owing to the combined effect of the antenna and the reflective environment. In the NLOS region, the contribution level of the strongest path becomes less dominant with increasing virtual Tx-Rx separation. The analysis of these results can be instructive for the deployment of a 60-GHz system in a reflective environment.