Multi-Cell MIMO Cooperative Networks: A New Look at Interference

Question

1. What is the standard technique to cope with inter-cell interference?

2. What are the Wyner models of cellular systems?

3. What is the mth BS able to decode?

4. What is the way to scale the per-cell sum-rate capacity?

Accepted Answer

A standard technique to cope with inter-cell interference is spatial reuse, that consists in activating at a given time (or equivalently in a given subband) only one cell every F ≥ 1 cells.

Accepted Answer

Wyner [9] introduced a linear array model, and a hexagonal cell model, which have become known as Wyner models of cellular systems, and these are very tractable for informationtheoretic analysis.

Accepted Answer

The mth BS can however decode an arbitrary linear combination∑Lk=−L bkxm−k with bk ∈ Z (and by symmetry bk = b−k) and b0 = 0 and treat the remaining part of the signal as Gaussian noise.

Accepted Answer

An important finding from such analysis is that, for large number K of users per cell, the per-cell sum-rate capacity scales as log log K , which is the same type of scaling as for interference-free systems.

Accepted Answer

The theoretical treatments of interference-limited channels on the one hand, and of cooperation protocols on the other hand, are still maturing, mostly due to the inherent complexity of the problem.

Accepted Answer

Other advanced techniques, not discussed here, such as interference alignment are also expected to have an important role to play in cooperative cellular systems (see, e.g., [72]).

Accepted Answer

a number of important practical issues must be addressed before a very realistic assessment of system gains can be made, such as the impact of imperfect synchronization between base stations, imperfect channel estimation at the receiver side, and network latency.

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This allows a non-interference limited behavior to be attained: Specifically, assuming that C grows like β log P, the multiplexing gain min(1, 0.5 + β) can be attained [41].

Accepted Answer

As a final remark, the optimal multiplexing gain of one is achieved if the backhaul capacity C scales as log P, which coincides with the optimal behavior predicted by the upper bound (13).

Accepted Answer

the authors assume that there is interference only between relays in adjacent cells, and that such interference is symmetric, so that T is a symmetric Toeplitz matrix with first row equal to [0 μ 0TM−2], where μ represent the inter-relay gains.

Accepted Answer

From the definition above, it is clear that, in general, H is a finite-band matrix (in the sense that only a finite number of diagonals have non-zero entries).

Accepted Answer

To evaluate RergMCP (P ), one can either use approximations based on bounding techniques as in [25] or the fact that, if FHH†(x) converges almost surely in some asymptotic regime of interest to some limiting distribution (spectrum) F (x), then RergMCP (P ) converges to (9c) with FHH†(x) = F (x) (see, e.g., [48]).

Accepted Answer

It was at that stage only that the downlink of the multi-cell cooperative channel, first investigated for the downlink in 2001 [12], was recognized to be almost identical to the so-called broadcast MIMO channel, if one ignores the power constraint at the individual base stations.

Accepted Answer

While fading puts limits on the coverage and reliability of any point-to-point wireless connection, e.g., between a base station and a mobile terminal, interference restricts the reusability of the spectral resource (time, frequency slots, codes, etc.) in space, thus limiting the overall spectral efficiency expressed in bits/sec/Hz/base station.

Accepted Answer

In [31], this scenario is considered, and a per-cell achievable sum-rate is derived for a strategy whereby the BSs simply compress (to C bits/channel use) and forward the received signals to the CP.

Multi-Cell MIMO Cooperative Networks: A New Look at Interference

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Most frequently asked questions

1. What is the standard technique to cope with inter-cell interference?

2. What are the Wyner models of cellular systems?

3. What is the mth BS able to decode?

4. What is the way to scale the per-cell sum-rate capacity?

5. Why are the theoretical treatments of interference-limited channels still maturing?

6. What are the other advanced techniques that are not discussed here?

7. What are the main issues that must be addressed before a realistic assessment of system gains can be?

8. What is the way to achieve a non-interference limited behavior?

9. What is the way to achieve the optimal multiplexing gain of one?

10. What is the symmetric matrix of interference between relays?

11. What is the definition of a finite-band matrix?

12. What is the way to evaluate RergMCP?

13. What was the first time that the downlink was recognized as being identical to the broadcast MIMO?

14. What is the main difference between interference and fading?

15. What is the simplest example of a per-cell achievable sum-rate?

Figures

Citations

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References

Elements of information theory

Capacity of Multi‐antenna Gaussian Channels

Capacity of Multi-Antenna Gaussian Channels

Layered space-time architecture for wireless communication in a fading environment when using multi-element antennas

Optimal decoding of linear codes for minimizing symbol error rate

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