Abstract
In this paper, we study upper bounds on the sum capacity of the downlink multicell processing model with finite backhaul capacity for the simple case of 2 base stations and 2 mobile users. It is modeled as a two-user multiple access diamond channel. It consists of a first hop from the central processor to the base stations via orthogonal links of finite capacity, and the second hop from the base stations to the mobile users via a Gaussian interference channel. The upper bound is derived using the converse tools of the multiple access diamond channel and that of the Gaussian MIMO broadcast channel. Through numerical results, it is shown that our upper bound improves upon the existing upper bound greatly in the medium backhaul capacity range, and as a result, the gap between the upper bounds and the sum rate of the time-sharing of the known achievable schemes is significantly reduced.
Highlights
The multi-cell processing system, as reviewed in [1], has been used to increase the throughput and to cope with the inter-cell interference
The following of this paper finds an upper bound on the sum capacity of the 2-user Gaussian multiple access diamond channel
NUMERICAL RESULTS To illustrate the tightness of the derived upper bound in Theorem 1, we plot and compare the existing simple cut-set upper bound on the sum capcity in (6), the new cut-set upper bound of (4), the new upper bound of Theorem 1, and the achievable sum rates of existing schemes for the 2-user Gaussian multiple access diamond channel
Summary
The multi-cell processing system, as reviewed in [1], has been used to increase the throughput and to cope with the inter-cell interference. The downlink multi-cell processing system, when first considered, consists of different base stations linked to the central processor via backhaul links of unlimited capacity, and the amount of cooperation among the different base stations is unbounded This network can be modeled by a MIMO broadcast channel and the sum-rate characterization was found in [2]. In the medium capacity region, there is still a relatively large gap between the simple cut-set upper bound and the performance of the time-sharing of the known achievable schemes It is unknown how well the proposed achievable schemes are and whether further efforts are needed in proposing better achievable schemes than existing ones for the downlink multicell processing system. Comparing numerically the proposed upper bound, the simple cut-set upper bound and the sum rate of various achievable schemes for the multicell processing system in terms of the sumrate, we see that our upper bound improves upon the existing simple cut-set upper bound greatly in the medium backhaul capacity range, and as a result, the gap between the upper bounds and the sum rate of the time-sharing of the known achievable schemes is significantly reduced
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