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Achievable Degrees of Freedom of the K-user MISO Broadcast Channel withAlternating CSIT via Interference Creation-Resurrection
Mohamed Seif, Amr El-Keyi, and Mohammed NafieWireless Intelligent Networks Center (WINC), Nile University
Objective• In this paper, we analyze the degrees offreedom for the K-user multiple-inputsingle-output (MISO) broadcast channel (BC)with synergistic alternating channel stateinformation at the transmitters (CSIT).
Specifically, the CSIT alternates between threestates, namely, perfect CSIT (P), delayed CSIT(D) and no CSIT (N). Each state is associatedwith a fraction of time denoted by λP , λD andλN , respectively.
Contribution•We propose a transmission scheme foralternating CSIT for the K-user BC.
•We show the benefit of the alternating CSITover delayed CSIT and other CSIT models(more details in the paper).
•The degrees of freedom for the K-user BC inour work is given by
DΣ(K) ≥ K2
2K − 1(1)
Introduction
An important performance measure for a communi-cation network is its degrees of freedom (DoF) whichdetermines the behavior of the sum capacity in thehigh signal-to-noise ratio (SNR) regime. In particu-lar, the network capacity under a transmission powerP is given by
C(P ) = DoF log(P ) + o(log(P )) (2)where limP→∞
o(log(P ))log(P ) = 0.
R1
R2
W11, W12
W11, W21
Transmitter1
W21, W22
Transmitter2
W12, W22
H11(t)
H12(t)
H21(t)
H22(t)
Figure 1: Two-user X channel model
Network Model
R1
RK
H1(t)
HK(t)
W1 ,..., WK
W1
WK
^
^
Transmitter with
K antennas
Figure 2: K-user BC channel model
System Model
•We consider a MISO broadcast channel with Ktransmit antennas and K single antenna receivers.The received signal at the ith receiver is given by
Yi(t) = Hi(t)X(t) + Ni(t), i = 1, . . . , K (3)
where X(t) is the K × 1 transmitted signal at timet with a power constraint E{|X(t)|2} ≤ P . Theadditive noise Ni(t) ∼ CN (0, 1) at time t generatedat receiver Ri is circularly symmetric white Gaus-sian noise with zero mean and unit variance. Hi(t)is the 1 × K channel vector from the transmitterto receiver Ri at time t which is sampled from acontinuous distribution whose elements are complexGaussian. The channel coefficients are assumed tobe i.i.d. across the receivers.
Results
1 2 3 4 5 6 7 8 9 101
1.5
2
2.5
3
3.5
4
4.5
5
5.5
K (users)
DoF
sum
(K)
CSIT with alternationCSIT with all delayed
Figure 3: DoF comparison for broadcast channel between alldelayed and alternating CSIT.
1 2 3 4 5 6 7 8 9 101
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
DoF
sum
(K)
K (users)
CSIT with all delayedCSIT with alternation
Figure 4: DoF comparison for X-channel between all delayedand alternating CSIT ([1,2]).
References
[1] A. Wagdy, A. Elkeyi, T. Khattab and M. Nafie, “On thesynergistic benefits of alternating CSIT for X channelwithin a four-symbol channel extension,” in Proc. IEEEICC, 2015.
[2] A.Wagdy, A.Elkeyi, and M.Nafie, “On the Degrees ofFreedom of SISO X-Channel with Alternating CSIT,” inProc. IEEE ISIT, 2015.
Contact Information•Email: [email protected]•Phone: +2 (0100) 694-6194
