Fundamentals of Multiplexing and Multiple Access Technologies

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Ἀλεξανδρεύς Ζαΐμης
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1 Tel: Fax: CDMA SNIR OFDM, MIMO Fundamentals of Multiplexing and Multiple Access Technologies Takaya YAMAZATO EcoTopia Science Institue, Nagoya University Furo-cho Chikusa-ku Nagoya, Tel: Fax: Abstract The paper introduces the fundamentals of multiplexing and multiple access (MA) technologies for mobile communication systems. We first provide a simple formulization of MA schemes through mathematical expression that is based on CDMA. Using the expression, three concepts of MA are introduced. We also introduce two important performance measures: signal to interference-and-noise ratio (SNIR) and spectral efficiency. Based on the discussion on MA, we then introduce multiplexing techniques. We focus on OFDM, multi-code transmission, and MIMO, known as high-speed transmission schemes based on multiplexing technique.

2 1 [1] multiple access: MA multiple access protocol Multiplexing frequency division multple acess: FDMA) time division multiple access: TDMA code division multiple accesss: CDMA space division multiple accesss: SDMA [2, 3] signal to interference-plus-noise ratio; SNIR spectral efficiency 1: OFDM, MIMO 2

3 1: 2: Frequency Division Multiple Access : FDMA PDC GSM Time Division Multiple Access: TDMA Code Division Multiple Access: CDMA Space Division Multiple Access: SDMA 1 FDMA TDMA TDMA a k (t) k multiple access function: MA function P b k (t) ω c a k (t) = 1 BPSK b k (t) b k (t) = m= b m,k p Tb (t mt b ) (2) b m,k { 1, 1} k m T b p x { 1, 0 t < x p x (t) = 0, otherwise (3) 1CDMA CDMA CDMA a k (t) T b a k (t)a k ( k)(t) ɛ (4) ɛ 2 k s k (t) s k (t) = a k (t) 2P b k (t) cos ω c t (1)

4 a 1 k cos(ω 1 t ) b (t) k a 2 k cos(ω 2 t ) s (t) k 1 T b a N f k cos(ω N t ) f 3: N f 5: MC-CDMA 4: DS-CDMA DS-CDMA DS-CDMA direct sequence code division multiple access a k (t) = a l kp Tc (t lt b ) (5) l= a l k { 1, 1} k i a k = {a 1 k, a2 k,, an k } DS-CDMA ɛ 0 ɛ = 0 CDMA time-synchronous CDMA 3 (a) a(t) f c = 1/T c b(t) f b = 1/T b DS-CDMA s(t) 4 2 (2f c ) BPSK sinc BPSK 2f b f c /f b N N = f c f b (6) N (spreading ratio) (processing gain) DS-CDMA N TDMA TDMA a 1 = {N, 0,, 0}, a 2 = {0, N, 0,, 0}, 3(b) CDMA MC-CDMA N f a k (t) = a l k cos(ω l t) (7) l=1 N f

5 1/T b ɛ CDMA multicarrier code division multiple access: MC-CDMA MC- CDMA MC-CDMA DS-CDMA [5, 6] (1 + N f ) 1 (1 + α) = T b T c 1 + N f = N(1 + α) (8) α DS-CDMA α = 0 MC-CDMA DS-CDMA FDMA FDMA TDMA MC- CDMA 2.3 a 1 = {N f, 0,, 0}, a 2 = {0, 0, N f, 0,, 0}, ɛ = SDMA 2.4.1,.,,,.,,,,,,,. 6(a) (b) A B 6: α n (t) n, τ n (t), n. 6(c) SDMA SDMA h(θ, τ; t) = p(θ)h(τ; t) (10) p(θ) θ angular spread 4 a k (t) = h k (θ k, τ k ; t) 4 ɛ = 0 SDMA CDMA TDMA h(τ; t) = n α n (t)e j2πfcτn(t) δ(τ τ n (t)) (9)

6 2.5 SNIR K r(t) r(t) = (11) K a k (t τ k ) 2P b k (t τ K ) cos(ω c t + φ k ) k=1 +η(t) η(t) τ k i τ i = φ i = 0) Z i = Tb 0 r(t)a i (t) cos ω c tdt (12) Z i = P/2b m,i T b (13) K Tb + a k (t τ)a i (t)dt cos φ k + k=1(k i) Tb 0 0 η(t)a i (t) cos ω c tdt Z i = ɛ multiple access interference : MAI SNIR SNIR signal to interference-and-nose ratio SNIR 1 ρɛ(k 1) + N 0 /2E b (14) E b N 0 ρ TDMA and FDMA: ɛ = 0 DS-CDMA: ɛ = 1 α/4 2N [4] 7: ρ MC-CDMA: ɛ = 1 2N f [5, 6] DS-CDMA α = 0 DS-CDMA MC-CDMA SNIR SNIR CDMA ɛ 14 ɛ(k 1) CDMA 14 ρ ρ = 1 ρ = 0 7 ρ [7]. ρ 0.45 ρ 0.05 ɛ ρ ρ 2.6 spectral efficiency

7 8: [1] η = K 1 W sys AC G [Erlang/m2 /Hz] (15) W sys [Hz] A[m 2 ] C G [Erlang/channel] C TDMA FDMA C = 3 C = 7 CDMA C = 1 K Quality of Service QoS 14) K W sys MIMO OFDM 1 AC G voice activation 9: CDMA r = 1/3, C/N 0 W s = 8[dB] 30 40% 40% CDMA FDMA TDMA AC FDMA TDMA 9 C = 1/4 CDMA CDMA FDMA TDMA 10 CDMA K W sys 8 CDMA FDMA TDMA K W sys (C/N 0 W s ) (r = 1 1/3) 10 5 (r = 1) CDMA 3 Multiplexing Frequency Division Multiplexing: FDM

8 T b 10: Time Division Multiplexing: TDM Code Division Multiplexing: CDM Space Time Multiplexing: STM multicarrier transmission orthogonal frequency division multiplexing: OFDM PHS W-CDMA multicode transmission space-time codes MIMO multiple-input multipl-output OFDM, MIMO 10(a) T b T b 10(b) T b inter-symbol interference: ISI +1, -1 T b T b T b 3.2 OFDM 1/T b orthogonal frequency division multiplexing: OFDM 7 a = {b m, b m+1,, b m+nf 1} k OFDM N f s(t) = b m+l 1 cos(ω l t) (16) l=1 11 OFDM IEEE802.11a OFDM IFFT FFT 3.1 T b

9 data FEC coder Interleaving + Mapping IFFT G.I. addition Symbol wave shaping IQ mod X HPA Transmitter b i,0 a 0 LNA X AGC IQ det. Trasmitter block diagram of OFDM PHY AFC clock recovery Remove G.I. FFT Reciver block diagram of OFDM PHY Demapping + Deinterleaving FEC coder data b M i S/P b i,1 b i,2 b i,(m-1) a 1 a 2 a M-1 IWHT Σ s M i =(s i,0,s i,1,s i,(m-1) ) PN gen. Amp. ωc 11: OFDM IEEE a Receiver Tc LPF PN gen. ωc s^ M i a 0 a 1 a 2 a M-1 WHT Σ Σ Σ Σ Ts z z z z i,0 i,1 i,2 i,(m-1) decision decision decision decision ^ b i,0 ^ b i,1 ^ b i,2 ^ b i,(m-1) P/S b ^ M i 13: 12: OFDM OFDM 16 OFDM N f OFDM N f OFDM OFDM DS-CDMA W-CDMA OFDM : OFDM 3.5 MIMO MIMO

10 15: MIMO [8] 15 MIMO N M MIMO t C t,n, n = 1, 2,, N N M MIMO MIMO h n,m m N r l,m = h n,m C t,n + η t,m (17) n=1 η t,m m 12 a k (t) MIMO h n,m space-time signal processing MIMO MIMO 4 CDMA DS-CDMA TDMA MC-CDMA FDMA SDMA SNIR SNIR CDMA OFDM, MIMO [1] Gordon L. Stuber, Principle of Mobile Communication, Kluwer Academic Publishers, [2] CDMA [3] CDMA Proc. of 2001 Microwave Workshops and Exhibition, MWE2001. [4] T. Shibata, M. Katayama and A. Ogawa, Performance of Asynchronous Band-Limited DS/SSMA Systems, IEICE Transaction on Communications, vol.e76-b, no.8, pp , Aug [5], CDMA,, vol.j85-a, no.3, pp , [6],,,, MC- CDMA SNIR, vol.j86-a, no.12, pp , [7] Zaher Dawy and Alexander Seeger, Coverage and Capacity Enhancement of Multiservice WCDMA Cellular Systems via Serial Interference Cancellation, Proc. of ICC, No. WC07-3, Jun., [8], Jounal of Signal Processing, Vol.8, No.3,

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