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IDMA (Interleave-Division Multiple-Access ) is a new method of digital communication that is very powerful and can approach the Shannon limit. The technique is very good for multiple user communication as is performed in a mobile phone connection from the phone to the basestation
In modern communication, Code Division Multiple Access (CDMA) has made its depth in wireless communication. CDMA offers well-known features: Dynamic channel sharing, soft capacity, reuse factor of one, low drop-out rate and large coverage (due to soft handover), ease of cellular planning, robustness to channel impairments and immunity against interference, etc. These advantages are due to spreading the information over a large bandwidth (“wideband transmission”). The performance of conventional CDMA systems is limited by multiple access interference (MAI), as well as intersymbol interference (ISI). Also, the complexity of CDMA multiuser detection has always been a serious concern. The problem can be seen from the angle of computational cost as well complexity of multiuser detection algorithms. The use of signature sequences for user separation is a characteristic feature for a conventional CDMA system. Interleaving is usually placed between forward error correction (FEC) coding and spreading and is traditionally employed to combat the fading effect. The possibility of employing interleaving for user separation in CDMA systems is possible but the receiver complexity is considered as a main obstacle. In journals a performance improvement achieved by assigning different interleavers to different users in a CDMA system is demonstrated. In journals, multiuser detection in narrowband applications with a small number of users is investigated.
A conventional random waveform CDMA (RWCDMA) system (such as IS-95) involves separate coding and spreading operations. Theoretical analysis shows that the optimal multiple access channel (MAC) capacity is achievable only when the entire bandwidth expansion is devoted to coding. This suggests combining the coding and spreading operations using low-rate codes to maximize coding gain. But separation of users without spreading operation is not feasible in CDMA.
One possible solution to this problem is to employ chip-level interleavers for user separation. This principle has been considered previously and its potential advantages have been demonstrated showing the possibility of employing interleaving for user separation in coded systems. For wideband systems, the performance improvement by assigning different interleavers to different users in conventional CDMA has been demonstrated in journals which studied a chip interleaved CDMA scheme and a maximal-ratio-combining (MRC) technique for ISI MACs. It clearly demonstrated the advantages of introducing chip-level interleavers. An interleaver-based multiple access scheme has also been studied in journalsfor high spectral efficiency, improved error performance and low receiver complexity.
This paper presents an asynchronous interleave-division multiple-access (IDMA) scheme for spread spectrum mobile communication systems, in which users are distinguished by different chip-level interleavers instead of by different signatures as in a conventional CDMA system incorporating the principle explained in journals. The scheme considered is a special case of CDMA in which bandwidth expansion is entirely performed by low-rate coding. For convenience, it may be referred as interleave-division multiple-access (IDMA). This scheme inherits many advantages from CDMA such as dynamic channel sharing, mitigation of cross-cell interferences, asynchronous transmission, ease of cell planning, and robustness against fading. It also allows a low complexity multiple user detection techniques applicable to systems with large numbers of users in multipath channels. In this paper, an effort has been made to study of proposed IDMA scheme by different researchers. A very low-cost chip-by-chip iterative detection algorithm is explained with complexity independent of user number and increasing linearity with the path number. The advantages of using low-rate coded systems are demonstrated analytically. We will show that the proposed IDMA scheme can achieve performance close to the capacity of a multiple access channel.
Does IDMA also improve SNR vs BER characteristics or just the capacity. Also I've observed the trend that 4G prospective technologies have iterative algorithms at the reciever. Does this provide any possible problem with practical implementation like power efficiency of the wireless device
Also do you have any suggestions regarding implementation of MIM0-OFDM-IDMA or something like that
Manoj,
Please dont 'copy and paste' the article u've got.Read the article, try to understand and write few points about what u've learnt.That will help u a lot and everyone appreciates u.
take care
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