Outline Multiuser Interference in TH-UWB Roman Merz, Cyril Botteron, Pierre-Andr´ e Farine Institute of Microtechnology University of Neuchˆ atel 2000 Neuchˆ atel Workshop on UWB for Sensor Networks, 2005 Merz, Botteron, Farine Multiuser Interference in TH-UWB
Outline Outline Introduction 1 Motivations and Goals Description TH-UWB Receiver Architecture Coherent Addition 2 No Timing Error Gaussian Jitter Frequency Offset Multiuser Interference 3 Definitions Single User Frame Non Synchronized Interference Frame Synchronized Interference Conclusions 4 Merz, Botteron, Farine Multiuser Interference in TH-UWB
Introduction Motivations and Goals Coherent Addition Description TH-UWB Multiuser Interference Receiver Architecture Conclusions Motivations and Goals Motivations A WSN may contain many nodes UWB is an attractive physical layer technology for WSNs Goals Evaluation of the applicability of a code sequence as a spreading code Evaluation during all receiver’s operating modes, including initial synchronization phase Merz, Botteron, Farine Multiuser Interference in TH-UWB
Introduction Motivations and Goals Coherent Addition Description TH-UWB Multiuser Interference Receiver Architecture Conclusions Impulse Radio No modulation, no spreading T s = N f T f Symbol composed of N f t frames Each frame contains one pulse Time Hopping Spreading (TH-UWB) A frame is formed by N c T s = N f T f chips t Pulse position determined by repetitive T f = N c T c spreading code with N f elements. Merz, Botteron, Farine Multiuser Interference in TH-UWB
Introduction Motivations and Goals Coherent Addition Description TH-UWB Multiuser Interference Receiver Architecture Conclusions Receiver Architecture A subsequence at the expected time of arrival � Subseq ◦ of a pulse is acquired Several subsequences are added to increase SNR T f Code T s Ref Pulse Further processing (correlation, demodulation) is not t t t considered The implementation may be in analog or digital domain Merz, Botteron, Farine Multiuser Interference in TH-UWB
Introduction Motivations and Goals Coherent Addition Description TH-UWB Multiuser Interference Receiver Architecture Conclusions Receiver Architecture Correlator with seq. of rectangular templates A subsequence at the expected time of arrival � Subseq ◦ of a pulse is acquired Several subsequences are added to increase SNR T f Code T s Ref Pulse Further processing (correlation, demodulation) is not t t t considered The implementation may be in analog or digital domain Merz, Botteron, Farine Multiuser Interference in TH-UWB
Introduction No Timing Error Coherent Addition Gaussian Jitter Multiuser Interference Frequency Offset Conclusions No Timing Error Pulse combining gain G PC (dB) No timing error: linear × × × × pulse combining gain 45 Theoretical × Measurement 40 × × G PC = N f 35 × × 30 Gaussian jitter: linear × × 25 pulse combining gain × 20 × × � 5 � 15 t n × G PC = N f × 10 � t 2 n + σ 2 × 5 × × Frequency offset: 0 × 2 0 2 5 2 10 2 15 non-linear pulse combining gain Number of coherent additions N f Merz, Botteron, Farine Multiuser Interference in TH-UWB
Introduction No Timing Error Coherent Addition Gaussian Jitter Multiuser Interference Frequency Offset Conclusions Gaussian Jitter Pulse combining gain G PC (dB) No timing error: linear 0 ps 100 ps pulse combining gain 45 200 ps 40 G PC = N f 35 30 Gaussian jitter: linear 500 ps 25 pulse combining gain 20 � 5 � 15 t n G PC = N f 10 � t 2 n + σ 2 5 Frequency offset: 0 2 0 2 5 2 10 2 15 non-linear pulse combining gain Number of coherent additions N f Merz, Botteron, Farine Multiuser Interference in TH-UWB
Introduction No Timing Error Coherent Addition Gaussian Jitter Multiuser Interference Frequency Offset Conclusions Frequency Offset Pulse combining gain G PC (dB) No timing error: linear 1 fs pulse combining gain 45 10 fs 40 G PC = N f 35 100 fs 30 Gaussian jitter: linear 25 pulse combining gain 1 ps 20 � 5 � 15 t n G PC = N f 10 � t 2 n + σ 2 5 Frequency offset: 0 2 0 2 5 2 10 2 15 non-linear pulse combining gain Number of coherent additions N f Merz, Botteron, Farine Multiuser Interference in TH-UWB
Introduction Definitions Coherent Addition Single User Multiuser Interference Frame Non Synchronized Interference Conclusions Frame Synchronized Interference Frame Synchronization Frame Synchronized and Code Synchronized T s δ User of interest → coherent t t addition w k w 1 , k w 2 , k w 3 , k w 4 , k Serves as a reference scenario for the evaluation Frame Synchronized Erroneous code (not user of interest or wrong code phase) Partially coherent addition Frame Non Synchronized Interferer with unrelated timing Merz, Botteron, Farine Multiuser Interference in TH-UWB
Introduction Definitions Coherent Addition Single User Multiuser Interference Frame Non Synchronized Interference Conclusions Frame Synchronized Interference Frame Synchronization Frame Synchronized and Code Synchronized Coherent Addition of the user of interest Serves as a reference scenario for the evaluation Frame Synchronized t t Erroneous code (not user of w k w 1 , k w 2 , k w 3 , k w 4 , k interest or wrong code phase) Partially coherent addition Frame Non Synchronized Interferer with unrelated timing Merz, Botteron, Farine Multiuser Interference in TH-UWB
Introduction Definitions Coherent Addition Single User Multiuser Interference Frame Non Synchronized Interference Conclusions Frame Synchronized Interference Frame Synchronization Frame Synchronized and Code Synchronized Coherent Addition of the user of interest Serves as a reference scenario for the evaluation Frame Synchronized Erroneous code (not user of interest or wrong code phase) Partially coherent addition Frame Non Synchronized t t w k w 1 , k w 2 , k w 3 , k w 4 , k Interferer with unrelated timing Merz, Botteron, Farine Multiuser Interference in TH-UWB
Introduction Definitions Coherent Addition Single User Multiuser Interference Frame Non Synchronized Interference Conclusions Frame Synchronized Interference Distinction Coefficient W (a) t t w k Maximum absolute value User of interest, synchronized w 1 , k w 2 , k w 3 , k w 4 , k Interferers W (b,c) t t w k Max (all configurations) Erroneous code w 1 , k w 2 , k w 3 , k w 4 , k Interferers Merz, Botteron, Farine Multiuser Interference in TH-UWB
Introduction Definitions Coherent Addition Single User Multiuser Interference Frame Non Synchronized Interference Conclusions Frame Synchronized Interference Distinction Coefficient W (a) t t w k D = W (a) / W (b,c) w 1 , k w 2 , k w 3 , k w 4 , k W (b,c) t t w k w 1 , k w 2 , k w 3 , k w 4 , k Merz, Botteron, Farine Multiuser Interference in TH-UWB
Introduction Definitions Coherent Addition Single User Multiuser Interference Frame Non Synchronized Interference Conclusions Frame Synchronized Interference Distinction Coefficient W (a) t t w k W (a) = N f max t q ( n ) ( t ) w 1 , k w 2 , k w 3 , k w 4 , k W (b,c) t t w k W (b,c) = S max max t q ( n ) ( t ) D = W (a) / W (b,c) w 1 , k w 2 , k w 3 , k w 4 , k Instead of correlating signals, counting the number of “hits” S max . (Valid if duration of the received pulse is shorter than a chip). Merz, Botteron, Farine Multiuser Interference in TH-UWB
Introduction Definitions Coherent Addition Single User Multiuser Interference Frame Non Synchronized Interference Conclusions Frame Synchronized Interference Results t u t u 8 LFSR t u u t 7 t u RAND 6 b b t u t u t u t u b t 4 bits 5 b b u D b 4 b t u t u b t u b b b b b b 3 bits 3 × u t × × × × × × × × × 2 × b t u b b c b c b × × 2 bits × × × c b c b c b b c b c b c c b b c b c c b c c b b 1 c b b c t u × c 1 bit 0 b 2 4 8 16 32 64 128 256 Code length N f Fig: D for LFSR and random spreading codes, without MAI, in PC Distinction coefficient depends on the code length N f and the number of bits to represent one element of the code. Merz, Botteron, Farine Multiuser Interference in TH-UWB
Introduction Definitions Coherent Addition Single User Multiuser Interference Frame Non Synchronized Interference Conclusions Frame Synchronized Interference Distinction Coefficient W (a) t t w k Expected value User of interest, synchronized w 1 , k w 2 , k w 3 , k w 4 , k Frame non synchronized interferers W (b,c) t t w k max over all expected values m th user w 1 , k w 2 , k w 3 , k w 4 , k all users � = m Merz, Botteron, Farine Multiuser Interference in TH-UWB
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