Signal-to-interference Plus Noise Power Ratio Research Articles

Maximum ratio combining for OFDM systems with cochannel interference

In this paper, we investigate a receive diversity combining method for orthogonal frequency division multiplexing wireless local area network systems with cochannel interference. The scheme utilizes interference plus noise power (INP) to obtain the weighting factors for signal to interference plus noise power ratio (SINR) based maximum ratio combining (MRC). INP is estimated by using the correlation between the subchannel gains within the coherence bandwidth of the channel, which is caused by the limited delay spread of the multipath channel. Simulation results show that the SINR based MRC using the proposed INP estimator reveals greatly improved packet error rate performance compared to the signal-to-noise ratio based MRC that only considers white channel noise.

A novel blind adaptive space-time receiver for multi-code DS-CDMA

Abstract-The capacity of conventional wireless communications systems based upon Direct-Sequence Code Division Multiple Access (DS-CDMA) schemes, is mainly limited by Multiple Access Interference (MAI). Therefore, methods aimed at reducing MAI are mandatory solutions to increase the capacity of such systems. Smart Antennas are a promising technology for improving the performance of high capacity mobile communications systems, because they are expected to be able to increase the Signal to Interference plus Noise power Ratio (SINR) of the received signals by dynamically adapting the equivalent array beam pattern in order to track the movements of the users within the cell. In this paper we propose a novel blind adaptive beamforming algorithm tailored for the up-link of multi-code multi-rate DS-CDMA wireless communications systems. Our proposal is based upon a modified Constant Modulus (CM) criterion, whose fundamental feature is the capability to overcome the main drawback of the classic CM algorithm, which lies in its difficulty of ensuring the convergence toward the desired user. The proposed algorithm exploits user-specific information intrinsically known at the receiver, which is the code uniquely associated to each user, without requiring the knowledge of the spatiotemporal propagation channel nor any specific training sequence. Within this paper we present a broadband solution, designed to temporally re-align uncorrelated clusters of multipaths, as well as spatially recombine correlated multipaths belonging to the same cluster. Computer simulations show that our proposed technique can effectively exploit path diversity and multipath correlation, also in the presence of Doppler effect and time-variable propagation conditions.

Performance Analysis of Polynomial Cancellation Coding for OFDM Systems over Time-Varying Rayleigh Fading Channels

Polynomial cancellation coding (PCC) was proposed to mitigate the sever inter-carrier-interference (ICI) in an orthogonal frequency division multiplexing (OFDM) system caused by frequency offset. In this paper, we consider the effectiveness of PCC under time-variant multi-path Rayleigh fading analytically and by simulations. We first consider an analytical expression of the signal-to-interference plus noise power ratio (SINR) and then derive an approximation of the bit-error-rate (BER) of the OFDM-PCC system under the assumption that ICI is well approximated by a white Gaussian noise. Since the bandwidth efficiency of OFDM-PCC is half of that of normal OFDM, we compare the BER performance of the scheme with the normal OFDM system of the same bitrate when low, medium, and high level modulations are used. Our results show that OFDM-PCC performs well even for high modulation level under time-varying multi-path fading.

Field Experiments on Throughput Performance above 100 Mbps in Forward Link for VSF-OFCDM Broadband Wireless Access

This paper presents throughput performance along with power profiles in the time and frequency domains over 100 Mbps based on field experiments using the implemented Variable Spreading Factor-Orthogonal Frequency and Code Division Multiplexing (VSF-OFCDM) transceiver with a 100-MHz bandwidth in a real multipath fading channel. We conducted field experiments in which a base station (BS) employs a 120-degree sectored beam'antenna with the antenna height of 50 m and a van equipped with a mobile station (MS) is driven at the average speed of 30 km/h along measurement courses that are approximately 800 to 1000 m away from the BS, where most of the locations along the courses are under non-line-of-sight conditions. Field experimental results show that, by applying 16QAM data modulation and Turbo coding with the coding rate of R = 1/2 to a shared data channel together with two-branch antenna diversity reception, throughput over 100 and 200 Mbps is achieved when the average received signal-to-interference plus noise power ratio (SINR) is approximately 6.0 and 14.0 dB, respectively in a broadband channel bandwidth where a large number of paths such as more than 20 are observed. Furthermore, the location probability for achieving throughput over 100 and 200 Mbps becomes approximately 90 and 20% in these measurement courses, which experience a large number of paths, when the transmission power of the BS is 10 W with a 120-degree sectored beam transmission.

An OFDM Based Adaptive Modulation Scheme Employing Variable Coding Rate

This paper proposes an OFDM based adaptive modulation scheme employing variable coding rate (VCR OFDM AMS), which selects optimum modulation and coding scheme (MCS) realized by combination of several modulation schemes and coding rates. The OFDM AMS with multilevel transmit power control (OFDM AMS/MTPC) can realize high data rate transmission in the dynamic parameter controlled-orthogonal frequency and time division multiple access (DPC-OF/TDMA). The employment of OFDM AMS/MTPC, however, makes transceiver design rather complex. To solve this problem, we propose to improve throughput performances of the OFDM AMS without employment of the MTPC. The simple OFDM AMS, however, does not fully utilize transmit power for throughput improvement because there is surplus transmit power which corresponds to power margin over required signal to interference plus noise power ratio (SINR). Thus, in order to improve transmit power efficiency for throughput increase, we reduce the required SINR gaps between adjacent MCSs by introducing many coding rates. Furthermore, this paper presents an effective bit loading algorithm when multiple coding rates as well as modulation schemes are used. Computer simulation confirms that the proposed VCR OFDM AMS gives sufficient throughput performances as an alternative to the OFDM AMS/MTPC.

Unified Packet Scheduling Method Considering Delay Requirement in OFCDM Forward Link Broadband Wireless Access

This paper proposes a unified packet scheduling method that considers the delay requirement of each traffic data packet whether real time (RT) or non-real time (NRT), the channel conditions of each accessing user, and the packet type in hybrid automatic repeat request (ARQ), i.e., either initially transmitted packet or retransmitted packet, in the forward link for Orthogonal Frequency and Code Division Multiplexing (OFCDM) wireless access. In the proposed packet scheduling method, the overall priority function is decided based on P Total = α Delay . P Delay + α Type . P Type + α SINR . P SINR (P Delay , P Type , and P SINR are the priority functions derived from the delay requirement, type of packet, and the received signal-to-interference plus noise power ratio (SINR), respectively, and α Delay , α Type , and α SINR are the corresponding weighting factors). The computer simulation results show that the weighting factor of each priority function as α Type /α Delay = 0.6, α SINR /α Delay = 0.4 assuming the linear-type function in P Delay and a constant-type function in P Type is optimized. Furthermore, we show that the outage probability for achieving the packet loss rate (PLR) of less than 10 -3 for non-real time (NRT) traffic users employing the proposed packet scheduling method is reduced by approximately two orders of magnitude compared to that using the Priority Queuing (PQ) method while maintaining the PLR of real-time (RT) traffic users at the same level as that using the PQ method.

One-cell reuse TDMA system using OFDM-based adaptive modulation and multilevel transmit power control schemes

OFDM AMS/MTPC (OFDM-based Adaptive Modulation Scheme with Multilevel Transmit Power Control) using multilevel transmit power control schemes to set the modulation levels and transmitted power of each subcarrier of an OFDM (Orthogonal Frequency Division Multiplexing) system can significantly improve the throughput in an isolated cell environment. This paper takes advantage of the property that OFDM AMS/MTPC allows high throughput by using the frequency selectivity of the received SINR (Signal to Interference plus Noise power Ratio) in the presence of interference, and a one-cell reuse TDMA (Time Domain Multiple Access) system using simple wireless resource control is proposed. In this system, it is necessary to limit dynamic variations of the interference power level associated with transmit power control in such a way that control of the OFDM AMS/MTPC can be appropriately carried out depending on the interference among the cells. In this paper, it is confirmed that an effective cell reuse value of 1.46 can be achieved by optimization with regard to the application of diversity reception, the control period of adaptive modulation, and the spacing of the required SINR of the modulation level. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(12): 50–60, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20195

A downlink beamforming method for multimedia CDMA/TDD systems

AbstractThis paper proposes a downlink beamforming method in TDD (time division duplex)‐type CDMA (code division multiple access) system. The proposed beamforming is a method that can satisfy various requirements of the user for SINR (signal‐to‐interference‐plus‐noise power ratio) in the multimedia communications environment while trying to minimize the total transmitted power from the base station. In the proposed method, the beamforming is performed with allowance for the SINR required by the user and the number of fingers in RAKE reception at the terminal. In the beamforming process it is desirable to reduce the total transmitted power from the base station in transmitted power control. As a result of performance evaluation, we see that the proposed method can improve the system capacity in an environment where terminals with various transmission rates coexist. In particular, when the traffic is concentrated to a cell, the proposed beamforming is shown to function effectively. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(6): 61–75, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10062

An adaptive space–time receiver for high‐capacity communications systems based on multichannel multirate DS‐CDMA

AbstractThe capacity of wireless communications systems based upon Direct‐Sequence Code Division Multiple Access (DS‐CDMA) is severely reduced by Multiple Access Interference (MAI), especially at higher bit rates. Therefore, methods aimed at limiting the MAI are mandatory solutions in order to face the ever‐growing number of subscribers of next‐generation wireless systems. Smart Antennas are a promising technology for improving the performance of high‐capacity mobile communications systems, because they are able to increase the Signal to Interference plus Noise power Ratio (SINR) of the received signals by dynamically adapting the equivalent array beam pattern in order to track the movements of the users within the cell. Moreover, Spatiotemporal RAKE receivers, representing the synergy between beamforming techniques and RAKE receiver structures, are one of the best candidates for the realization of high‐capacity multichannel (CDMA) wireless systems, due to their ability in exploiting both the spatial and temporal diversity inherently offered by wireless channels.This paper is focused on the structure of a Spatiotemporal RAKE receiver for the uplink of multichannel DS‐CDMA systems. Its main feature is the capability of coherently combining the multipaths of the useful signal across both space and time, while simultaneously reducing the MAI. A blind and adaptive beamforming algorithm realizing such a Spatiotemporal RAKE receiver is presented. It exploits the knowledge and the synchronization of the scrambling code uniquely assigned to an addressed user, requiring neither estimates of the spatiotemporal propagation channel nor training or pilot sequences. Its design philosophy consists in the maximization of the SINR at the beamformer output, and it is based upon an orthogonal projection of the received signal onto the linear space generated by the spreading code of the desired user.Computer simulations show the effectiveness of the Spatiotemporal receiver, in terms of convergence speed, SINR gain and bit error probability. Copyright © 2002 John Wiley & Sons, Ltd.

Optimal receive antenna polarization in the presence of interference and noise

The receive antenna polarization that maximizes the signal-to-interference-plus-noise power ratio (SINR) for an arbitrarily polarized signal is determined in the presence of arbitrarily polarized interference and thermal noise. The derivation makes use of the Poincare sphere representation of polarization and reduces the optimization problem to solution of a single transcendental equation. SINR performance is given in terms of degradation from the polarization matched, noise only case. Finally, a comparison of this optimum-pol strategy, with pol-nulling the interferer and pol-matching the signal is presented. These results provide insight into applying polarization theory to improve signal reception in the presence of interference and thermal noise. >