Adaptive Multicarrier CDMA Space-Time Receivers - Adaptive Signal Processing in Wireless Communications - page 288

BER performance is not sufficient because the data rate is not equal for all configura-
tions. Hence, we translate the link-level results into system-level results in terms of total
throughput under the following three assumptions: (1) all users are received with an
equal average power (i.e., - D and - I ) [4]; (2) all the cells have the same average load of
C users per cell; and (3) the out-cell to in-cell interference ratio f is set to 0.6 [47]. Given
these assumptions in an interference-limited system (thermal noise is low compared to
interference), the link-level SIR at the base station antennas (ignoring ISI for simplicity)
is

1

SIR = , (10.4 4)

ISR

1

( ) + () + ( ) +

C 1 αδχβ ρρκ 1 Cf λ

is λ ξ

L

where

() = ()

   

χβ max χβ ,

kk

1

( ) + ( )

= () + ()

ας βχβ ρ λ ξ 1 κ , (10.45)

L

1
L

( )

= () + ()

γ ς βχβκ .

( C - 1)α is the normalized variance of the residual MAI ( u ≠ d ), 1 L δ is χ(β) (1 + ρ λ - ρ ξ )κ - is
the normalized variance of the residual ICI ( k ′ ≠ k and u = d ), and Cf γ is the normalized
variance of the out-cell interference. Note that equation (10.44) is derived from equation
(10.41) and the assumption of negligible thermal noise and ISI.
The maximum number of users that can access the system C max can be hence cal-
culated by the simple procedure illustrated in Table 10.1 . After initialization, this pro-
cedure increments the capacity C , until the SIR ISR given by equation (10.44) no longer
exceeds the required SNR req . he SRN req is the required SNR, derived from link-level
simulations, to meet a BER of 5% in order to achieve a QoS of 10 -6 after channel decod-
ing. In step 2.2 of Table 10.1, we use the fact that the SIR expression applies to MRC by
setting κ - = 1 and ρ λ = ρ ξ = 0 in equation (10.44). In step 2.3, we evaluate the symbol error
rate S MRC after the MRC stage as follows:

= ( )

S MRC Ω SIR, (10.4 6)

MRC

where Ω represents the single-user bound (SUB). Note that multistage MC-ISR is con-
sidered in step 2.5. The total throughput is hence T max = C max × R b = C max × R s × log 2 (M)
where R b and R s are the bit rate and symbol rate over all subcarriers, respectively.

10.3.4 MC-ISR Receiver Implementation
As mentioned in section 10.3.2, the proposed MC-ISR receiver requires accurate chan-
nel parameter estimates and data decisions to reconstruct the total interference Î k,n and