Conference Paper

ISI analysis in network MIMO OFDM systems with insufficient cyclic prefix length

Dept. of Mobile Commun. Syst., Tech. Univ. Dresden, Dresden, Germany
DOI: 10.1109/ISWCS.2010.5624259 Conference: Wireless Communication Systems (ISWCS), 2010 7th International Symposium on
Source: IEEE Xplore

ABSTRACT

We consider a cellular network MIMO OFDM system where cooperating base stations apply joint signal processing to the receive signals of several users. In this situation, due to geometry, the problem of unavoidable differences in time of arrival between the users' signals occurs. As a result, symbol timing offsets can be larger than the cyclic prefix, which leads to OFDM inter-symbol interference. In addition to the multiuser interference, a coupling between adjacent subcarriers and consecutive OFDM symbols is induced in such scenarios. In this paper, we analyze the multi-user joint detection performance in systems with distance dependent asynchronous interference and pathloss environments for different channel delays as well as fixed cyclic prefix length. To this end we use an exact expression for the post equalization SINR that is used for the evaluation in numerical simulations. The system level cell setup considers two user positioning models based on a hexagonal cell geometry with varying cell radii.

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    • "An analytical framework for the calculation of the interference due to an insufficient CP as well as hardware-related impairments is given in[14]. While all these references are focused on a SISO (single-input single-output) system, the interference due an insufficient CP length is studied in[15]for a network MIMO (multiple-input multiple-output) system. Due to the temporal variation of the channel, the interference power due to an insufficient CP length varies over different OFDM packets. "
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    ABSTRACT: The performance of OFDM systems over a multipath channel can strongly degrade due to the propagation delay spread. The distortion of the received signal over the fast Fourier transform window is referred to as multipath noise. This work aims to analytically determine the performance loss due to multipath noise as a function of OFDM and channel parameters for narrowband OFDM systems. First, it is investigated whether it is possible to describe the multipath noise, varying over different OFDM packets due to the temporal variation of the channel, by an effective noise factor $F_{rm delay} $, from which the loss factor is directly determined. Second, the theory of room electromagnetics is applied to develop a closed-form expression for $F_{rm delay} $ as a function of the OFDM and reverberation parameters. This analytical method is validated with excellent agreement. Finally, the loss factor is determined for IEEE 802.11 based on channel measurements in two large conference rooms, providing values up to 19 dB for an 800 ns cyclic prefix length.
    Preview · Article · Mar 2015 · IEEE Transactions on Wireless Communications
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    • "technique proposed in [9] adds redundancies in the frequency domain by adding unused subcarriers. Some other techniques have been also proposed in [1]–[3], [5], [6], [8]. "
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    ABSTRACT: In this paper, a channel independent precoding for MIMO-OFDM systems of $n_t$ transmit and $n_r$ receive antennas with insufficient cyclic prefix (CP) is proposed. By empolying the interference alignment (IA) idea, we show that our proposed channel independent precoding scheme can eliminate the inter-block interference (IBI) caused by the insufficient CP with a higher bandwidth efficiency than the conventional zero-padding or adding a sufficient CP when $n_r\leq n_t$. It is also shown that when $n_r>n_t$, the IBI can be eliminated without any zero-padding or adding CP or precoding when the OFDM block length is not small.
    Preview · Conference Paper · Jan 2011
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    ABSTRACT: We consider coordinated multi-point systems where multiple base stations apply a joint signal processing in the uplink and downlink. Large distances between the base stations result in unavoidable differences in time of arrival between the users' signals which in turn lead to inter-symbol interference in OFDM systems if the cyclic prefix length is exceeded. Moreover, carrier frequency offsets which are caused by imperfect oscillators lead to inter-carrier interference and are in particular a problem in the downlink due to the feedback delay of the measured channel state information. In this paper we derive metrics for evaluating the impact of time and frequency asynchronisms in CoMP systems with large base station distances. We compare performance results for CoMP and single user transmission techniques in a selected transmission scenario where we use a 3GPP/LTE baseline system.
    Preview · Conference Paper · Jun 2011
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