Advanced Spread Spectrum Topics -- PN & Gold Codes, LFSR Sequences, Multipath Fading, OQPSK/MSK/GMSK Modulation, and More

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Spread Spectrum & CDMA Resources

A comprehensive directory of spread spectrum resources, including tutorials & theory, circuit diagrams, OEM products, development tools, test equipment, and more.

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Advanced Spread Spectrum Topics

Spread Spectrum Systems & Theory

PN Codes & LFSR Generators

(Kasami sequences; Barker, Walsh, Gold codes, ...)

Correlation, Correlators, & Despreading

General PN Synchronization

PN Code Acquisition

PN Code Tracking

Modulation Techniques

(OQPSK, MSK, GMSK, ...)

Multipath Fading

(a.k.a. Raleigh Fading)

Spread Spectrum Systems & Theory

Spread Spectrum			Top
Witold Jachimczyk Worcester Polytechnic Institute Electrical and Computer Engineering Department
This is an impressive summary of the many aspects of spread spectrum communication systems, starting with a brief history, and then digging right down into the details of direct sequence, frequency hopping, and time hopping. It gives detailed overviews of these technologies and explores their respective strengths and weaknesses. It including several block diagrams and just enough math to make the article interesting and informative, but not overwhelming for the average engineer. While a bit worn and forgotten (e.g. some non-essential graphics, like bullets, are missing), it is one of the better articles available for the serious student.

Non-Cellular Wireless Communication Systems			Top
Jacobus Petrus Franciscus Glas 1996 Doctoral Thesis Delft University of Technology, The Netherlands
The focus of Dr. Glas' thesis is the design of a CDMA spread spectrum transceiver operating in the license-free 2.4 GHz ISM band -- and to make the system inexpensive enough to compete with conventional cell phones. Anybody browsing through Dr. Glas' thesis is bound to find something of interest. And, while the document is rather voluminous, the hierarchically arranged table-of-contents makes it a snap to locate any particular area of interest.

The World of CDMA - An Overview of IS-95			Top
Dr. Arthur Ross CDMA Development Group
The best CDMA One (IS-95) tutorial we've encountered, this white paper offers a complete technical overview of the IS-95 standard, including considerations of capacity and coverage so important to CDMA, the near-far problem, multipath fading, and much more. The article is appropriate for those with a technical background but unfamiliar with spread spectrum in general or CDMA in particular. Lots of graphics, just a little math.

An Overview of IS-95 and cdma2000 (PDF)			Top
Unknown Author Unknown Organization
Note: This document is currently unavailable at its original URL. It has reportedly been included in a new book on CDMA. You might consider doing a search for the title at Google.com to see if it has re-posted somewhere on the Web. This is one of the best CDMA One (IS-95) and cdma2000 tutorials we have encountered, in terms of offering not only a general outline and history of the systems, but also detailed block diagrams and explanations of how the two systems work. The article is so easy to read, yet so comprehensive, that we have included it in both the Primers and Advance Topics sections of our Spread Spectrum Resources directory. However, it is best suited for those who already have a basic understanding of spread spectrum and CDMA principles.

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PN Codes, PRBS Sequences, & LFSR Generators
(Including Kasami, Walsh, Gold codes, etc.)

LFSR Reference - PRBS Generator Implementation, M-Sequences, M-Sequence Properties, & Feedback Taps			Top
Engineering Staff New Wave Instruments
This handy reference and tutorial covers both the Galois and Fibonacci implementations of linear feedback shift register (LFSR) PRBS generators, as well as the definition and properties of m-sequences, and how to determine m-sequence feedback taps. But the best part is that you won't have to determine feedback taps -- just look them up in the supplied tables!

Spreading Sequences			Top
Byoung Jo Choi University of Southampton, United Kingdom Mobile Multimedia Research Group
A concise and easy-to-understand discussion of the properties of the various spreading codes used in spread spectrum and CDMA systems. Techniques for generating the codes aren't covered, and there isn't a lot of detailed information. But a wide variety of codes are covered: Gold codes, Kasami codes, Walsh codes, multi-rate orthogonal Gold codes, Shapiro-Rudin PN codes, Sivaswamy's complementary sequence sets, and poly-phase sequences (Frank and Zadoff-Chu sequences).

Spread Spectrum 2: Codes, Processing Gain, and Synchronization			Top
Maurice Schiff, Ph.D. www.TechOnline.com
If you scroll down to Part 3 ("P3"), you will find some useful information on the generation and properties of PN codes, Gold codes, Kasami codes, Walsh codes, and Barker codes. There is also a good discussion on synchronization. Unfortunately, the figures are difficult to make out.

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PN Correlation, Correlators, & Despreading

All About Correlators			Top
Randy Roberts RF/SS Consulting
More of a practical paper than scholarly, this article will appeal more to "real" RF designers than to PhDs. It touches lightly on several correlation techniques, including the well known sliding correlators, tau-dither and delay-locked/early-late-detection loops. It also covers analog techniques, involving the use of double-balanced mixers, SAW, and CCD devices, and digital techniques using ASIC devices.

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General PN Code Synchronization

Carrier and Code Synchronization			Top
Jacobus Petrus Franciscus Glas 1996 Doctoral Thesis, Synchronization Section Delft University of Technology, The Netherlands
This is the Synchronization section of Dr. Glas' 1996 doctoral thesis, which covers the design of a CDMA spread spectrum transceiver operating in the 2.4 GHz ISM band, referred to as wissce. Though the document clearly targets this particular transceiver, it provides valuable insight into the challenges of code acquisition and tracking in general, and compares the advantages and disadvantages of various techniques. Plenty of block diagrams and plots are presented, making the article particularly easy to follow.

Spreading Code Acquisition and Tracking (PDF)			Top
Tan F. Wong University of Florida Wireless Communications Laboratory
This textbook-style tutorial covers both PN acquisition and tracking. The different forms of acquisition explored are serial search, parallel search, multi-dwell detection, and matched filter. Miss and false alarm rates, and acquisition time, are discussed extensively, with enough mathematical analysis to satisfy any post-graduate student. Finally, code tracking is explored in the form of an early/late gate delay-locked loop (DLL). The article includes a number of useful block diagrams.

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PN Code Acquisition

Spreading Code Acquisition and Tracking (PDF)			Top
Tan F. Wong University of Florida Wireless Communications Laboratory
This textbook-style tutorial covers both PN acquisition and tracking. The different forms of acquisition explored are serial search, parallel search, multi-dwell detection, and matched filter. Miss and false alarm rates, and acquisition time, are discussed extensively, with enough mathematical analysis to satisfy any post-graduate student. Finally, code tracking is explored in the form of an early/late gate delay-locked loop (DLL). The article includes a number of useful block diagrams.

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PN Code Tracking

Spreading Code Acquisition and Tracking (PDF)			Top
Tan F. Wong University of Florida Wireless Communications Laboratory
This textbook-style tutorial covers both PN acquisition and tracking. The different forms of acquisition explored are serial search, parallel search, multi-dwell detection, and matched filter. Miss and false alarm rates, and acquisition time, are discussed extensively, with enough mathematical analysis to satisfy any post-graduate student. Finally, code tracking is explored in the form of an early/late gate delay-locked loop (DLL). The article includes a number of useful block diagrams.

The Delay Locked Loop	(Reprint)	Top
James A. Vincent
A brief but highly informative overview of delay-locked loops, also known as an early-late detection loops. If you have trouble with the page staying loaded, try clicking on Reprint, above.

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Modulation Techniques (GMSK, MSK, OQPSK, etc.)

The Evolution from BPSK to GMSK (PDF) (a.k.a. Appendix D – Digital Modulation and GMSK, from the report entitled "Electromagnetic Compatibility Aspects of Radio-based Mobile Telecommunication Systems")			Top
University of Hull, United Kingdom Personal Communications Programme
This well written and illustrated document explores the logical path from the elementary BPSK modulation scheme, to QPSK, to OQPSK, to MSK, and finally to GMSK modulation. Each of these modulation schemes is briefly described and explored, and the reasoning behind each step in the succession is presented. Visual plots of each scheme is provided, making it easy for anyone to understand even MSK and GMSK in a matter of minutes.

QPSK Modulation vs. GMSK Modulation (PDF) (a.k.a. Linear vs. Constant Envelope Modulation Schemes in Wireless)			Top
Ambreen Ali, Felicia Berlanga The University of Texas at Dallas
This easy-to-understand student paper outlines and compares the properties of the QPSK and GMSK modulation schemes, and touches lightly on how they relate to other modulation types: BPSK, QAM, and MSK. Block diagrams of the two schemes are provided, as are various time and power-spectral-density plots.

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Multipath Fading

Characterization of Rayleigh Fading (PDF) (a.k.a. Rayleigh Fading Channels in Mobile Digital Communication Systems, Part I: Characterization)			Top
Bernard Sklar Communications Engineering Services
This is Part I of a two-part scholarly tutorial on multipath (Rayleigh) fading, primarily in the UHF band, that affects mobile systems such as cellular and personal communication systems (PCS). Part I itemizes the fundamental multipath fading manifestations and types of degradation. Part II, below, focusses on methods for coping with multipath fading.

Mitigation of Rayleigh Fading (PDF) (a.k.a. Rayleigh Fading Channels in Mobile Digital Communication Systems, Part II: Mitigation)			Top
Bernard Sklar Communications Engineering Services
In Part I of this tutorial, above, the major elements that contribute to multipath fading and their effects in a communication channel are characterized. Here, in Part II, these phenomena are briefly summarized, and emphasis is then placed on methods to cope with these degradation effects. Two particular mitigation techniques are examined: the Viterbi equalizer implemented in the Global System for Mobile Communication (GSM), and the Rake receiver used in CDMA systems built to meet Interim Standard 95 (IS-95).

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Relevant Search Terms

For the benefit of those searching the Web, following are search terms relevant to this page:

Spread Spectrum Topics:

Barker Code, Correlator, De-Spread, De-Spreads, Delay Lock Loop, Delay Lock Loops, Despread, Despreads, DSSS, FHSS, Generation, Gold Code Generator, Gold Codes, Gold Sequence, Gold Sequences, Kasami Code, Kasami Sequence, LFSR, Linear Recursive Sequence, Linear Recursive Sequences, Lock, LRS, M-Sequence, M-Sequences, Offset QPSK, Orthogonal Code, Orthogonal Codes, Orthogonal Gold Code, Orthogonal Gold Codes, Orthogonal Spreading Code, Orthogonal Spreading Codes, PN Code Correlation, PN Code Generator, PN Code Synchronization, PN Code Tracking, PN Codes, PN Correlation, PN Sequences, PN Tracking, PRBS, Preferred Pair, Preferred Pairs, Pseudo-Noise Code, Pseudo-Noise Sequences, Pseudonoise Code, Pseudonoise Codes, Pseudonoise Sequences, Pseudo-Random Binary Sequence, Pseudo-Random Bit Sequences, Pseudo-Random Sequences, Pseudorandom Sequence, Sliding Correlator/Tracker, Staggered QPSK, Sliding Correlator, Synchronization, Synchronize, Synchronizer, Tracker, Walsh Code, Walsh Codes

RF & Microwave Topics:

AWGN, Autocorrelation, Bit Error Rate (BER), Channel, Cross-Correlation, Demodulation, Demodulator, Frequency, Multipath Fading Channel, MSK Modulation, OQPSK Modulation, QAM Modulation, Rayleigh Fading Channel, Signal to Noise Ratio (SNR)

Resources:

Basic, Basics, Block Diagram, Circuit Diagram, Fundamentals of, How to, Introduction to, Technique, Techniques, Tutorial, Tutorials, What is, White Paper, White Papers

British Equivalents:

Synchronise, Synchroniser, Synchronisation