Error analysis and lowcost error correction for the

Error analysis and low-cost error correction for the crowded wireless 2. 4 GHz band Mark Grossman ’ 11, Jens Mache Lewis & Clark College 1. Introduction 2. Our experiment Sensor networks • • are an “Emerging Technology That Will Change the World“ [1] • are distributed systems of small networked sensors • allow for an instrumentation of the physical world at an unprecedented scale and density • enable new generations of applications and the "Internet of Things" Wireless communication • most sensor networks use the 802. 15. 4 standard (Zig. Bee, etc. ) • operate in the 2. 4 GHz ISM (industrial, scientific, and medical) band • are subject to interference from other devices such as Wi-Fi (802. 11 a/b/g/n), Bluetooth devices, video devices, cordless phones, car alarms, child monitors and microwave ovens We developed code to monitor radio traffic between 802. 15. 4 -compliant devices. We constructed an experiment in which a standardized packet was broadcast from one device at a constant rate. A second device (operating in promiscuous mode) received these packets and determined if the packet contained errors. If the packet was erroneous, further analysis was performed to classify the error pattern into one of several 0000 - 20 41 c 8 99 03 00 ff ff-37 38 00 00 01 4 f 14 00 0010 - 7 f 69 40 00 0 a 54 45 53 -54 49 4 e 47 31 32 33 ab 0020 - 9 a 20 : Length c 8 41 : Frame Control Field 99 : Sequence Number 00 03 : Destination PAN ff ff : Destination Address 00 14 4 f 01 00 00 38 37 : Source Address 7 f 69 40 00 0 a 54 45 53 54 49 4 e 47 31 32 33 : MAC Payload 9 a ab : Frame Control Sequence A. . . 78. . . O. . . i@. . TESTING 123. . categories. 0000 - 23 41 c 8 d 1 53 00 ff ff-37 38 00 00 01 4 f 14 00 #A. . S. . . 78. . . O. . 0010 - 7 f 69 40 00 0 a 54 45 53 -54 49 4 e 47 31 32 33 af . i@. . TESTING 123. 0020 - ce 71 7 a 8 a . qz. ERR_LENGTH ***** 0000 - 20 41 c 8 6 b 03 00 ff ff-37 38 00 00 01 4 f 14 00 A. k. . 78. . . O. . 0010 - 7 f 69 40 00 0 a 54 45 53 -54 49 4 e 47 31 32 33 55 . i@. . TESTING 123 U 0020 - b 6 . ERR_DSN_OR_FCS ***** 0000 - 20 41 c 8 de 03 00 ff ff-37 38 00 00 01 4 f 14 00 A. . . 78. . . O. . 0010 - 7 f 69 40 00 0 a 54 45 53 -44 49 4 e 47 31 32 33 41 . i@. . TESDING 123 A 0020 - f 4 . ERR_SINGLE (24) ***** Error control • The standard method to deal with transmission errors is retransmission, also known as automatic repeat request (ARQ). • Sensor networks have to minimize communication in order to improve energy consumption and thus lifetime (batteries cannot be replaced). • Our long-term goal is to investigate (and develop) an alternative to ARQ: correcting bit errors using Cyclic Redundancy Checks (CRCs) which are already present and used for error detection. • e. g. for polynomial x 3 + x + 1, CRC(1000000) = 5. • Thus, error correction table T = { correct, 7, 6, 4, 5, 1, 3, 2 }. 0000 - 20 41 38 bb 03 00 ff ff-37 38 00 00 01 4 f 14 00 A 8. . . 78. . . O. . 0010 - 7 f 69 40 00 0 a 54 45 53 -54 49 4 e 47 31 32 33 cc . i@. . TESTING 123. 0020 - 04 . 4. Analysis & Conclusions Our results showed that the proportion of correctable errors was significant ERR_HALFBYTE (4) (~35%) and, furthermore, perhaps fewer than 5% of the remaining errors ***** could be corrected with an existing, expensive error correction scheme (FEC). 0000 - 20 41 c 8 2 a 03 00 ff ff-37 38 00 00 01 4 f 14 00 A. *. . 78. . . O. . This data enabled our colleague [2], who is implementing the error 0010 - 7 f 69 40 00 0 a 54 45 53 -54 49 4 e 47 31 52 65 23 . i@. . TESTING 1 Re# correction algorithm, to optimize his methods for the greatest amount of 0020 - 34 4 error correction with the least amount of overhead. ERR_EXTENDED (10) This experiment could be repeated under different conditions to determine ***** 0000 - 20 41 c 8 e 4 03 00 ff ff-37 38 00 00 01 4 f 14 00 A. . . 78. . . O. . 0010 - 7 f 69 40 00 0 a 54 65 65 -55 62 75 24 35 54 06 01 . i@. . Tee. Ubu$5 T. . 0020 - 30 0 ERR_MULTI (28) Acknowledgements & References ***** 0000 - 20 41 c 8 73 77 77 -77 77 A. swwwwww • If 1100010 transmits as 1101010, CRC = 3. 0010 - 77 77 -77 77 37 32 33 59 wwwwww 723 Y • T[3] = 4 correctly indicates that bit 4 was corrupted. 0020 - 44 D ERR_MULTI (96) the error profiles of various environments. This work is supported by an NSF REU and grant CNS-0720914. [1] MIT Technology Review, “ 10 Emerging Technologies That Will Change the World” [2] Travis Mandel & Jens Mache, Investigating CRC Polynomials that Correct Burst Errors, Proceedings of the International Conference on Wireless Networks, 2009