ECE 4371 Fall 2017 Introduction to Telecommunication EngineeringTelecommunication

ECE 4371, Fall, 2017 Introduction to Telecommunication Engineering/Telecommunication Laboratory Zhu Han Department of Electrical and Computer Engineering Class 18 Nov. 6 th, 2017

Outline l CDMA(code division multiple access) – – – Introduction FHSS(frequency hopping spread spectrum) DSSS(direct sequence spread spectrum) Application Road map

Spread Spectrum Modulation Techniques l Definition: – The bandwidth of the transmitted signal is much greater than the bandwidth of the original message. – The bandwidth of the transmitted signal is determined by the message to be transmitted and by an additional signal known as the Spreading Code. Two main Spread Spectrum modulation techniques l – Frequency Hopping Spread Spectrum (FHSS) – Direct Sequence Spread Spectrum (DSSS) l Two major advantages: – Low power density – Redundancy

Spread Spectrum Transmission l A spread-spectrum transmission offers three main advantages over a fixed-frequency transmission: – Spread-spectrum signals are highly resistant to noise and interference. u The process of re-collecting a spread signal spreads out noise and interference, causing them to recede into the background. – Spread-spectrum signals are difficult to intercept. – Spread-spectrum transmissions can share a frequency band with many types of conventional transmissions with minimal interference.

Spread Spectrum Transmission – Spread-spectrum signals are difficult to intercept. u u A spread-spectrum signal may simply appear as an increase in the background noise to a narrowband receiver. An eavesdropper may have difficulty intercepting a transmission in real time if the pseudorandom sequence is not known. – Spread-spectrum transmissions can share a frequency band with many types of conventional transmissions with minimal interference. u u The spread-spectrum signals add minimal noise to the narrow-frequency communications, and vice versa. Therefore, bandwidth can be utilized more efficiently.

Outline l CDMA(code division multiple access) – – – Introduction FHSS(frequency hopping spread spectrum) DSSS(direct sequence spread spectrum) Application Road map Hedy Lamarr

Frequency Hopping Spread Spectrum l Definition – A method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver. l Military use – Highly resistant to deliberate jamming – Limited protection u l The JTIDS/MIDS family, HAVE QUICK and SINCGARS Civilian use – In the unregulated 2. 4 GHz band

Frequency Hopping Pattern l A transmitter "hops" between available frequencies according to a specified algorithm. l The transmitter operates in synchronization with a receiver, which remains tuned to the same center frequency as the transmitter.

System Structure

Pseudo Random Sequence Generator l Random sequence – – l Randomness and noise properties Provide signal privacy Two properties – Randomness and unpredictability. l Pure randomness is hard to achieve. – Pseudorandomness, the sequences produced are long and there is no way of predicting the next number from the sequence.

Pseudo Random Sequence Generator l Linear Feedback Shift Registers(LFSR). – LFSR are implemented as a circuit consisting of XOR gates and shift register. – The register is a string of 1 -bit storage devices. l The m+1 th bit is output as the result of an operation on the previous m bits in the register. l By using a long enough sequence of bits, the sequence may appear to be random, even though it is actually a long cycle. ECE 4371 Fall 2008

FHSS Resistance of Jamming l Narrow band jamming l FHSS under broadband jamming l FHSS under partial band jamming – Jamming on one frequency affects only a few bits

Multiple User Access l Only one user with a large bandwidth is too wasteful. l Allows multiple user to be admitted over the same frequency. – This creates the possibility of system data rates that are higher than the Shannon limit for a single channel. l Each transmitter is assigned a unique code which allows multiple users to be multiplexed over the same physical channel.

Multiple User Access l Well designed PN sequence can prevent user collision. l In practice, collision cannot be avoided – Lack of a common synchronization clock – More than L active users access

Outline l CDMA(code division multiple access) – – – Introduction FHSS(frequency hopping spread spectrum) DSSS(direct sequence spread spectrum) Application Road map

Compare with FHSS l FHSS adopts noncoherent detection (FSK) l DSSS adopts coherent detection (QAM, PSK, PAM)

Direct Sequence Spread Spectrum l Modulates with a continuous string of pseudo-noise code symbols called "chips", each of which has a much shorter duration than an information bit. l Spreading code spreads signal across wider frequency band – In proportion to number of bits used – 10 bit spreading code spreads signal across 10 times bandwidth of 1 bit code l Spreads the bandwidth of the data uniformly for the same transmitted power.

Spreading & Despreading l Spreading – Source signal is multiplied by a PN signal l Processing Gain: l Despreading – Spread signal is multiplied by the spreading code l Polar {± 1} signal representation

Direct Sequence Spread Spectrum l One method: – – Combine input with spreading code using XOR Input bit 1 inverts spreading code bit Input zero bit doesn’t alter spreading code bit Data rate equal to original spreading code

Multiple User Access l Unique code to differentiate all users l Sequence used for spreading have low cross-correlations l Allow many users to occupy all the frequency/bandwidth allocations at that same time

Narrowband Interference Suppression Transmitt er Receiver

Wideband Interference Suppression Transmitt er Receiver

Outline l CDMA(code division multiple access) – – – Introduction FHSS(frequency hopping spread spectrum) DSSS(direct sequence spread spectrum) Application Road map

Application l FHSS – Bluetooth – frequency-hopping code division multiple access (FH-CDMA) l DSSS – CDMA – GPS – WLAN

Bluetooth l Operates in the globally unlicensed (but not unregulated) Industrial, Scientific and Medical (ISM) 2. 4 GHz short-range radio frequency band.

CDMA Rake Receiver

Comparison

GPS l Why spread spectrum in GPS ? – Signal from satellite can be kept from unauthorized use. – Inherent processing gain of spread spectrum allows reasonable power levels to be user. – Each satellite can use the same frequency band, yet no mutual interference.

WLAN l Why spread spectrum in WLAN ? – Operates in the range of 2. 4 GHz short-range radio frequency band. – Interference resistance from other wireless device

Outline l CDMA(code division multiple access) – – – Introduction FHSS(frequency hopping spread spectrum) DSSS(direct sequence spread spectrum) Application Road map

Cellular Telephony Evolution 1 G 2 G 2. 5 G 3 G 3. 9 G 4 G Analog voice telephony Digital voice telephony (9. 6 kbps-14. 4 kbps) Digital voice telephony data connectivity Built-in self organizing mechanisms broadband data connectivity IP based protocol for voice and data No data connectivity CDMA, TDMA Example: AMPS 1981 Example: GSM, IS-54, IS-95 A, cdma. One 1992 ECE 4371 Fall 2008 Example: GPRS, IS 958, IS-136, (E)-GPRS 1999 Example: WCDMA, CDMA 2000 TD-SCDMA 2001 Mobile broadband data connectivity Example: LTE 2007 Interference mitigation and coexistence Example: LTEAdvanced 2011

2 G: IS-95 A (1995) l Known as CDMAOne l Chip rate at 1. 25 Mbps l Convolutional codes, Viterbi Decoding Downlink (Base station to mobile): – Walsh code 64 -bit for channel separation – M-sequence 215 for cell separation l l Standard IS-95, ANSI J-STD-008 Multiple Access CDMA Uplink Frequency 869 -894 MHz Downlink Frequency 824 -849 MHz Channel Separation 1. 25 MHz Modulation Scheme BPSK/QPSK Number of Channel 64 Channel Bit Rate 1. 25 Mbps (chip rate) Uplink (Mobile to base station): – M-sequence 241 for channel and Speech Rate Data Rate user separation 8~13 kbps Up to 14. 4 kbps Maximum Tx Power 600 m. W

2. 5 G: IS-95 B (1998) l Increased data rate for internet applications – Up to 115 kbps (8 times that of 2 G) l Support web browser format language – Wireless Application Protocol (WAP)

3 G Technology l l Ability to receive live music, interactive web sessions, voice and data with multimedia features Global Standard IMT-2000 – CDMA 2000, proposed by TIA – W-CDMA, proposed by ARIB/ETSI Issued by ITU (International Telecommunication Union) l Excellent voice quality l Data rate – 144 kbps in high mobility – 384 kbps in limited mobility – 2 Mbps indoor l l Frequency Band 1885 -2025 MHz Convolutional Codes Turbo Codes for high data rates

3 G: CDMA 2000 (2000) l CDMA 1 x. EV-DO – peak data rate 2. 4 Mbps – supports mp 3 transfer and video conferencing l CDMA 1 x. EV-DV – Integrated voice and high-speed data multimedia service up to 3. 1 Mbps Channel Bandwidth: l – 1. 25, 5, 10, 15 or 20 MHz l l Chip rate at 3. 6864 Mbps Modulation Scheme – QPSK in downlink – BPSK in uplink

3 G: CDMA 2000 Spreading Codes l Downlink – Variable length orthogonal Walsh sequences for channel separation – M-sequences 3 x 215 for cell separation (different phase shifts) l Uplink – Variable length orthogonal Walsh sequences for channel separation – M-sequences 241 for user separation (different phase shifts)

3 G: W-CDMA (2000) l Stands for “wideband” CDMA l Channel Bandwidth: – 5, 10 or 20 MHz l Chip rate at 4. 096 Mbps Modulation Scheme – QPSK in downlink – BPSK in uplink l l Downlink – Variable length orthogonal sequences for channel separation – Gold sequences 218 for cell separation l Uplink – Variable length orthogonal sequences for channel separation – Gold sequences 241 for user separation

Road Map 1 XRTT/3 XRTT CDMA (IS 95 A) IS 95 B GSM GPRS W-CDMA TDMA EDGE UWC-136 cdma 2000 1999 2000 2001 2002 3 X cdma. One IS-95 A IS-95 B 1 X No 3 X 2 G 2. 5 G 3 G Phase 1 3 G Phase 2