Efficient Adaptive Modulation Technique for MAC-PHY Cross Layer Optimization in OFDMA-based Cellular Systems An adaptive transmission scheme using QAM and LDPC code is proposed for an OFDMA cellular system employing FDD. Also, adaptive algorithms for active user selection, subchannel transmission power allocation, and modulation and coding set selection were proposed. The performance of the proposed scheme was obtained from computer simulation and was compared with that of the conventional scheme using mean SNR only. It is shown that the proposed scheme can provide up to 5.0dB gain over the conventional scheme at the expense of only 3 more bits in feedback information. Keywords: Adaptive Transmission, OFDMA, LDPC I
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P pilot III
x x k k yahxn, (1)
A 2 h n 2 σ 2 zz i jz q zh * yhahxn', (2) n'h * nh 2 σ 2 z Ahx 2 σ 2 x 0 Λ(x 0 ) Λ(x 0 )log ( Σ Pr{zh,x}Pr{x} ) log ( Σ Pr{zh,x}Pr{x} ) xx 0,0 xx 0,1 (z i v) 2 (z q v) 2 (z i v) 2 (z q v) 2 log ( exp ( ) exp ( 2σ )) 2 2σ 2 (z i v) 2 (z q v) 2 (z i v) 2 (z q v) 2 log ( exp ( ) exp ( )), 2σ 2 2σ 2 (z i v) 2 (z i v) 2 2σ 2 2σ 2 2vz i (3) σ 2 X k,l k l vah2x 0 0z i v σ 2 Λ(x 0 ) 2v 2 σ 2 A 2 h 2 σ 2 4v 2 σ 2 2A 2 h 2 σ 2 Λ(x 1 ) L h l, l0,... L1 1 L2 A 2 h l 1 E{Λ(x k )x k 0} Σ 2m SNR L l0 σ 2 1 L1 2A 2 h l 2 A 4 h l 4 E{Λ 2 (x k )x k 0} Σ ( ) L l0 σ 2 σ 4 Var{Λ(x k )x k 0}E{Λ 2 (x k )x k 0}E 2 {Λ(x k )x k 0} 1 L1 2A 2 h l 2 A 4 h l 4 Σ ( L l0 σ ) 2 σ 4 1 L1 A 2 h l 2 ( Σ ) 2 L l0 σ 2 1 L1 2A 2 h l 2 1 L1 A 2 h l 2 2 Σ Σ ( L l0 σ ) 2 L l0 σ 2 1 L1 A 2 h l 2 2 ( Σ L l0 σ ) 2 4m SNR 4σ 2 SNR, (4)
m SNR σ 2 SNR 1 L1 A 2 h l 2 m SNR Σ, L l0 2σ 2 1 L1 A 2 h l 2 2 1 L1 A 2 h l 2 2 σ 2 SNR Σ ( ) ( Σ ). (5) L l0 2σ 2 L l0 2σ 2 - - Λ(x 0 )log ( Σ Pr{zh,x}Pr{x} ) xx 0,0 log ( Σ Pr{zh,x}Pr{x} ) xx 0,1 log(max xx 0,0 Pr{zh,x}Pr{x}) log(max xx 0,1 Pr{zh,x}Pr{x}) Euclidean distance differenceσ 2. (6) A 2 h 2 A 2 h 2 σ 2 E{Λ(x k )x k 0} m SNR Var{Λ(x k )x k 0} am SNR bm 2 SNR cσ 2 SNR (7)
σ SNR σ SNR m SNR IV m SNR σ SNR l P pilot m l,snr σ l,snr l P pilot K1(0,...,K) k
SNR k k (σ SNR ) l k P l,k P l,k P pilot SNR k m l,snr k (σ l,snr ) (8) SNR k k (σ SNR ) P c l,k P c l,k P pilot SNRc k m l,snr (9) SNR c k k S k * arg max r(k) subject to P 1,k P A,Max (10) k r(k) k P A,Max X P A,Max P S,Max P A,Max S l
k(l)arg max r(k) subject to P l,k P S,Max (11) k S l * (s)s1s k(l * (s)) for s1:s l * (s)arg max k(l); k(l * (s))0; l end for (12) X P S,Max P A,Max s {l * (s), k(l * (s))s1,..., S}arg max Σ r(k(l(s))) l(1),..., l(s) s1 s subject to Σ P l(s), k(l (s)) P A,Max (13) s1
Initialize: P (s)p l*(s),k(l*(s))+1 P l*(s),k(l*(s)) ; P (s)p l*(s),k(l*(s)) P l*(s),k(l*(s))-1 ; S r(k)r(k1)r(k); P l,k+1, P l,0 0, P r P A,Max Σ P l*(s),k(l*(s)) ; s1 While v arg max P (s); v arg min P (s); s s If( P (s)p r ) P r P r P (v ); k(l * (v )); Update P (v ), P (v ); elseig (( r(k(l * (v ))) r(k(l * (v ))1) & P (s)p r P (s)) or ( r(k(l * (v ))) r(k(l * (v ))1) & P (s) P (s))) P r P r P (v ) P (s); k(v );k(l * (v )); Update P (v ), P (v ), P (v ), P (v ); else break; endif; end while; P r
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