Guard interval

About: Guard interval is a research topic. Over the lifetime, 1615 publications have been published within this topic receiving 19658 citations.

Design and performance of multicarrier CDMA system in frequency-selective Rayleigh fading channels

Abstract: This paper presents the advantages and disadvantages of a multicarrier code-division multiple-access (MC-CDMA) system. The transmitter/receiver structure and, the bandwidth of transmitted signal spectrum are compared with those of a conventional direct-sequence (DS) CDMA system, and an MC-CDMA design method, how to determine the number of subcarriers and the length of guard interval is discussed. The bit error rate (BER) lower bounds for DS-CDMA and MC-CDMA systems are derived and their equivalence is theoretically demonstrated. Finally, the BER performance in downlink and uplink channels with frequency-selective Rayleigh fading is shown by computer simulation.

Interchannel interference analysis of OFDM in a mobile environment

Abstract: Orthogonal frequency division multiplexing with a suitably chosen guard interval is an effective means of eliminating intersymbol interference for high-rate transmission over fading dispersive channels. Time variations of the channel, however, lead to a loss of subchannel orthogonality, resulting in interchannel interference (ICI). The article examines the effects of ICI through analysis and simulation, in the context of a system design for HDTV digital video broadcasting to mobile receivers. It is shown that ICI can be modeled as an additive Gaussian random process that leads to an error floor which can be determined analytically as a function of the Doppler frequency. Antenna diversity and trellis coding are then examined as methods for reducing this error floor.

Random access in a mobile telecommunications system

Abstract: An uplink common physical channel (random access channel) frame structure is disclosed with a separate preamble and data portion. The preamble is used by a base station to detect that a mobile station is attempting a random access request. The data portion of the channel includes user data, and pilot symbols that provide energy for channel estimation during reception of the data portion. A guard interval (TG) is preferably inserted between the preamble and data portion of the frame, which enables data detection to occur during an idle period. As such, the frame structures for both the common physical (random access) uplink channel and dedicated physical (traffic) uplink channel are compatible.

Orthogonal frequency division multiplexing: a multi-carrier modulation scheme

Abstract: This paper presents a multi-carrier digital modulation technique-orthogonal frequency division multiplexing. A review of the technique and its development and implementation are provided. The advantages and disadvantages in comparison to other modulation techniques are also discussed. The ideas of using a guard interval to accommodate long delay ghosts and of creating spectrum notches to combat co-channel interferences, as well as of assigning different order of modulations or power levels to different sub-carriers for layered services are discussed. The effects of phase noise and the peak-to-average power ratio of the OFDM signal are also analysed. >

Performance analysis of OFDM systems for broadband power line communications under impulsive noise and multipath effects

Abstract: The impulsive noise and multipath effects are the main reasons to cause bit errors in power line communications. In this paper, the bit error rate (BER) performance of the orthogonal frequency division multiplexing (OFDM) system under the impulsive noise and multipath effects are theoretically analyzed in terms of closed form formulas. Through the analysis, it is shown that OFDM can mitigate the adverse effect of the impulsive noise and only the heavily disturbed impulsive noise will interfere the BER performance of the OFDM system. It is also shown that the adverse effect of multipath is more serious than that of impulsive noise. In this paper, the guard interval is used to improve the BER performance of the OFDM system. As the longer guard interval is inefficient in using the signal power, the optimum guard interval that can achieve the best BER performance is studied.