The document analyzes the degrees of freedom (DoF) for the K-user multiple-input single-output (MISO) broadcast channel with alternating channel state information at the transmitters (CSIT). It proposes a transmission scheme where CSIT alternates between perfect, delayed, and no CSIT states. The scheme achieves a DoF of K^2/(2K-1), which is higher than models with only delayed CSIT. Comparisons of the DoF between the proposed alternating CSIT scheme and existing delayed CSIT schemes are presented for the broadcast channel and X-channel models.

1. Achievable Degrees of Freedom of the K-user MISO Broadcast Channel with
Alternating CSIT via Interference Creation-Resurrection
Mohamed Seif, Amr El-Keyi, and Mohammed Nafie
Wireless Intelligent Networks Center (WINC), Nile University
Objective
• In this paper, we analyze the degrees of
freedom for the K-user multiple-input
single-output (MISO) broadcast channel (BC)
with synergistic alternating channel state
information at the transmitters (CSIT).
Specifically, the CSIT alternates between three
states, namely, perfect CSIT (P), delayed CSIT
(D) and no CSIT (N). Each state is associated
with a fraction of time denoted by λP , λD and
λN, respectively.
Contribution
• We propose a transmission scheme for
alternating CSIT for the K-user BC.
• We show the benefit of the alternating CSIT
over delayed CSIT and other CSIT models
(more details in the paper).
• The degrees of freedom for the K-user BC in
our 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) which
determines the behavior of the sum capacity in the
high signal-to-noise ratio (SNR) regime. In particu-
lar, the network capacity under a transmission power
P 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 K
transmit 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 time
t with a power constraint E{|X(t)|2
} ≤ P. The
additive noise Ni(t) ∼ CN(0, 1) at time t generated
at 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 transmitter
to receiver Ri at time t which is sampled from a
continuous distribution whose elements are complex
Gaussian. The channel coefficients are assumed to
be i.i.d. across the receivers.
Results
1 2 3 4 5 6 7 8 9 10
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
K (users)
DoFsum
(K)
CSIT with alternation
CSIT with all delayed
Figure 3: DoF comparison for broadcast channel between all
delayed and alternating CSIT.
1 2 3 4 5 6 7 8 9 10
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
DoFsum
(K)
K (users)
CSIT with all delayed
CSIT with alternation
Figure 4: DoF comparison for X-channel between all delayed
and alternating CSIT ([1,2]).
References
[1] A. Wagdy, A. Elkeyi, T. Khattab and M. Nafie, “On the
synergistic benefits of alternating CSIT for X channel
within a four-symbol channel extension,” in Proc. IEEE
ICC, 2015.
[2] A.Wagdy, A.Elkeyi, and M.Nafie, “On the Degrees of
Freedom of SISO X-Channel with Alternating CSIT,” in
Proc. IEEE ISIT, 2015.
Contact Information
• Email: m.seif@nu.edu.eg
• Phone: +2 (0100) 694-6194