By Mike Buehrer, William Tranter
This publication covers the elemental points of Code department a number of entry or CDMA. It starts with an creation to the fundamental principles at the back of mounted and random entry structures which will exhibit the variation among CDMA and the extra broadly understood TDMA, FDMA or CSMA. Secondly, a overview of uncomplicated unfold spectrum strategies are awarded that are utilized in CDMA platforms together with direct series, frequency-hopping and time-hopping methods. the elemental suggestion of CDMA is gifted, via the 4 simple ideas of CDMA structures that impression their functionality: interference averaging, common frequency reuse, gentle handoff, and statistical multiplexing. the point of interest of the dialogue will then shift to functions. the most typical program of CDMA at the moment is mobile platforms. an in depth dialogue on mobile voice platforms in line with CDMA, in particular IS-95, is gifted. The capability of such structures might be tested in addition to functionality enhancement options resembling coding and spatial filtering. additionally mentioned are 3rd iteration CDMA mobile platforms and the way they range from moment new release platforms. A moment program of CDMA that's lined is unfold spectrum packet radio networks. eventually, there's an exam of multi-user detection and interference cancellation and the way such ideas influence CDMA networks. This ebook may be of curiosity and price to engineers, complicated scholars, and researchers in communications.
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Additional resources for Code Division Multiple Access (CDMA)
6. 15) Thus, the PSD of the DS/SS BPSK signal is Sbp ( f ) ≈ P Tc 4 where P is the bandpass power. 4: Comparison of original/despread signal and spread signal spectra for DS/SS with square pulses. 2 Multiple Access The DS/SS technique can be expanded to multiple users by providing different spreading codes a k (t) to each user in the system where a k (t) is the spreading code of the kth user. 5. Channels are thus defined by the spreading waveform a k (t). Ideally, we would like all channels to be orthogonal.
46) i=1 where αi , f i , θi , and τi are the amplitude, Doppler shift, phase shift, and delay associated with the ith path. Note that the amplitudes of the paths are typically assumed to be normalized such that the channel has unit average gain. , non-resolvable) but large relative to a single cycle of the carrier frequency. 16: Performance of narrowband BPSK in AWGN and flat Rayleigh fading (DS/SS provides the same performance in an AWGN channel). 9 radians. When multipath components combine non-coherently, they have the potential of annihilating each other.
There are two basic spread spectrum techniques: direct sequence spread spectrum (DS/SS) and frequency-hopped spread spectrum (FH/SS) [1, 19, 20]. These two techniques can be used for multiple access and are commonly termed DS-CDMA and FH-CDMA. 3) and discuss their performance in AWGN and fading channels as well as their multiple access capabilities. Both techniques rely on spreading waveforms to accomplish pseudo-random spreading. A key to CDMA is defining multiple spreading waveforms with low cross-correlation properties to allow multiple users to share the spectrum efficiently.