Abstract
We introduce a novel merger of direct sequence code division multiple access (DS-CDMA) and smart antenna arrays. With regard to the DS-CDMA scheme, we employ carrier interferometry DS-CDMA (CI/DS-CDMA), a novel implementation of DS-CDMA where chips are decomposable into N narrowband frequency components. With regard to the antenna array, we deploy the oscillating-beam smart array. Here, applying proper time-varying phases to the array elements, we create small movement (oscillation) in the antenna array's pattern, while steering the antenna pattern main lobe to the position of the intended user. The oscillating antenna pattern creates a time-varying channel with a controllable coherence time. This, in turn, provides transmit diversity in the form of a time diversity gain at the mobile receiver side. At the receiver, three stages of combining are available: combining time components of the received signal within symbol duration Ts (each experiencing a different fade) to enhance performance via time diversity; combining frequency components which make up the CI/DS-CDMA chip to enhance the performance via frequency diversity; and combining across chips to eliminate the interfering users on the system. Merging CI/DS-CDMA with the oscillating-beam smart antenna at the base station, we achieve very high capacity via the merger of SDMA (available through directionality of the antenna array) and code division multiple access (inherent in CI/DS-CDMA), and very high performance via the construction of receivers that exploit both transmit diversity and frequency diversity. We present the performance gains of the proposed merger.
Highlights
Antenna arrays located at the base station (BS) enhance wireless communication systems via (1) directionality, which supports space division multiple access (SDMA); or (2) more recently, a transmit diversity benefit, that is, a diversity scheme that uses the antenna array at the BS to exploit diversity at the mobile
Assuming (a) rich scattering environment, (b) fully loaded CI/direct sequence code division multiple access (DS-CDMA) with a processing gain of N = 32 (i.e., K = 32 orthogonal users are available in the system), and (c) 4-fold frequency diversity over the entire bandwidth, simulation results demonstrate that the proposed system achieves 14 dB gain over a CI/DS-CDMA system with a conventional smart antenna array at a probability of error of 10−3
CI/DS-CDMA signals are sent via a single antenna array at the BS, and received by a single antenna at the mobile station
Summary
Antenna arrays located at the base station (BS) enhance wireless communication systems via (1) directionality, which supports space division multiple access (SDMA); or (2) more recently, a transmit diversity benefit, that is, a diversity scheme that uses the antenna array at the BS to exploit diversity at the mobile (see, e.g., [1, 2]). We innovatively apply the oscillating-beam antenna arrays of [3, 4, 5, 6] to DS-CDMA systems with CI chip shapes (CI/DS-CDMA) of [9, 10, 11, 12, 13] This enables (1) very high capacity via the merger of SDMA (directionality of the antenna array) and CDMA (inherent in CI/DS-CDMA); and (2) very high performance via the construction of receivers that exploit both transmit diversity and frequency diversity. Assuming (a) rich scattering environment (where, up to 7-fold time diversity is achievable via beam pattern movement [5, 6]), (b) fully loaded CI/DS-CDMA with a processing gain of N = 32 (i.e., K = 32 orthogonal users are available in the system), and (c) 4-fold frequency diversity over the entire bandwidth, simulation results demonstrate that the proposed system achieves 14 dB gain over a CI/DS-CDMA system with a conventional smart antenna array at a probability of error of 10−3. Referring to (3) and Figure 1, the CI chip shape corresponds to a frequency sampled version of the sinc(·) shape
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