|Title of Invention||
A SPREAD SPECTRUM TRAINER
|Abstract||The present invention relates to a method and apparatus for decoding a convolutionally encoded channel. The certainties of transmitted bits at predetermined locations in time are determined a priori. This information is then used to set the states of a Viterbi decoder to different state metrics in accordance with the certainties of the transmitted bits. High certainty of a transmitted bit results in resetting the states corresponding to that bit to a high state metric. In contrast, low certainty of a transmitted bit results in resetting the states corresponding to that bit to a low state metric. Resetting the states to different state metrics improves the decoding performance and shortens the time required to converge the decoding trellis by eliminating improbable paths.|
This invention relates to a spread spectrum
The spread spectrum communication concept has revolutionised global communication systems today. It has made a great breakthrough in wireless communications systems including telecom, computer networks, global positioning systems (GPS), personal communication systems (PCS), cellular, wireless local loop (WLL) and so on.
There is therefore a necessity to train, teach and understand the basic principles and concepts of spread spectrum communication by way of carrying out experiments and demonstration.
As a consequence of achieving the foregoing objective, there will be an increase in technical manpower In this field to cater to the needs of design, engineering, integration, testing, maintenance of spread spectrum communication systems in industries, education, research and development and so on.
Accordingly, the object of this invention Is to propose a spread spectrum trainer which will al low
training, teaching and a thorough understanding of the principle©, concepts and propertiem of spread spectrum and spread spectrum communication by experiments and demonstration 9 allow understanding of the principles of real-world applications like WLAN, CDMA in cellular and so on; allow projects to be carried out, prototypes to be made using the spread spectrum trainer as a central platform; be cost—effective to the user; and user-friendly.
The spread spectrum trainer proposed herein is of modular construction with the various components thereof, which require study, constituting buiIding blocks for the user.
Thus, the electrical connections to the modules can be altered with a purpose in mind for examining and studying either the input to, or the output of, any module or modules, as for Instance, by displaying the input or output on an Osci1loscope, by connecting, disconnecting, bypassing , substituting, adding-on and buiIding-up of a module or modules and examining the effect of such alteration, by connecting a module or modules while still in circuit, to external equipment in
order to observe the result or build prototypes of other equipment, such as, wireless 1 an and so on, using the spread spectrum trainer as a central platform; or build equivalent modules with different techniques or algorithms.
The modules themselves will have, wherever possible, means for varying the parameters thereof, so that the trainee will be enabled to better understand the working of the module and its impact on other components of the system.
Various other features of this invention will be apparent from the following further description thereof given hereunder.
The spread spectrum trainer proposed herein enables the study of both the major types of spread spectrum concepts, namely, the direct sequence spread spectrum (D9SS) and the frequency hopping spread spectrum (FHSS).
The spread spectrum trainer, according to this invention, comprises at least one transmitter and at 1 east one receiver characterised by a plurality of interconnected modules adaptable for
both 0886 and FH8S techniques, said modules comprising code generators; data generators and decoders) spreaders; frequency synthesizers; BPBK/FSK modulators; multlpath simulators; noise source; costas loop; delayed lock loop; and RF transmitter and RF receiver, together with means for altering the module connections and means for configuring the modules for varying the parameters thereof -
This invention will now be described with reference to the accompanying drawings which illustrate, by way of example, one of various embodiments of the spread spectrum trainer proposed herein,
Fig.i i1 lustrating the layout diagram of the spread spectrum trainer
Figs 2 and 3 respectively i1 lustrating the layout diagrams of the transmitter and receiver in further detail
Fig. 4 illustrating the important modules in the DSSS receiver (costas loop & DLL)
Fig.S i1lustrating the display section of the spread spectrum trainer, the store and display
Fig.6 11lustrating the user interface block diagram of the spread spectrum trainer
Fig. 7 illustrating a view of one of various possible front panels of the housing of the said embodim4»nt, as it would appear externally.
There are four code generators which can be configured to various parameters but with common length. This generator Is capable of generating all the commonly used code types (MAXIMAL, BOLD, BARKER and WALSH). It also gives the epoch (start of sequence) signal output for the data synchronisation.
The user can program these generators through keypad. The codes generated by these generators can be either taken to the spreader or can be used for external add-ons or can be left unused.
The important parameters of the code generator that can be configured are s
♦ Ini tial phase
Data generator module has an internal generator which generates a square wave form and a PROS of length IS. This module also has two codecs which can code two audio signals, three RS232 translators and a synchronizer for enternal data usage. Epoch signal generated by the code generator is used for synchronisation in all the processes.
The two audio signals are taken from the telephone handset which wi11 be connected to the spread spectrum trainer.
All the received signals are decoded at the decoder block back to the original data.
There are four spreaders for four users. Each
spreader modulates the generated code over data. The outputs of the spreader can go to BPSK modulator or multipath simulator through jumper settings.
The frequency synthesiser is of the direct digital frequency type (DDFS) driven by a crystal oscillator. This DDFS is controlled by a 8031 microcontroller. It generates all the necessary clocks (code clock, data clock and IF)
The BPSK modulator consists of double balanced mixers Which modulate the IF carrier with the spread data. There are four such modulators to accommodate four users. The output of the modulators is summed linearly to set the composite CDMA signals.
FSK modulation is done by the DDFS used in the clock generator (frequency synthesi zer) for frequency hopping.
The multipath simulator module introduces fi xed delays in spread data. The possible delays are 1/4 1/2 3/4. To generate delays of 1 5/4 3/2 7/4 and so on, the second code generator wi11 also
spread the same data but with 1 chip delay which is accomplished by changing the initial phase of the code. Therefore the delay with respect to the second spread data will be in addition to 1 chip delay.
The user can also vary the strength of the signal using a potentiometer. The inverted delayed spread data is also available.
The noise source generates a single tone jamming noise at IF, a Gaussian noise at base band and a Gaussian noise at IF. The user can select any on© of the three noises and it can be added along with the received signal. Basically, this is to demonstrate the noise rejection properties of the spread spectrum technique.
The costas loop is implemented digitally to achieve the carrier synchronisation. It synchronises the local oscl11 ator signal to th© incoming signal. This loop is realised using FGPAs and a DSP. The loop parameters 1 ike bandwidth and gain can be programmed by the user.
The del ay locked loop tracks the code that is used
for spreading. This loop is enabled only after
the code is acquired (coarse tuning) so that it
fine tunes the receiver code. This block also
enjoys the same flexibility of costas loop due to
DSP in the spread spectrum trainer.
The frequency hopping transmitter makes use of DDFS to generate hopping frequencies. A code generator controls the hopping pattern. The user is also to select either 15 or 31 frequencies as hopping frequencies. The hopping is done at IF.
The receiver is implemented digitally. The RF signal is down converted to IF uihich is digitized and fed to a pair of non-coherent demodulators uihich will detect the databit.
The RF transmitter converts the IF signal from the spread spectrum trainer to RF in ISM band. It consists of a radio frequency VCO, Up converter, power amplifier and an antenna.
The RF receiver unit converts back the RF to IF and feeds into the spread spectrum trainer. It consists of a down converter, BPF and LPF and an antenna. The other parameters wil1 match the the
The spread spectrum trainer will be provided uii th a user interface diagram clearly showing the modules involved and the signal flow in transmitter and receiver to assist the trainee in obtaining a quick and better understanding of the entire spread spectrum trainer- The trainer will also be provided wi th a user manual wi th structured experimenting procedures.
A LCD display panel (20 x 2), 10 element BAR LEDs and key pad will be used for configuring the spread spectrum trainer. The user can program all the parameters by going through a menu driven display and select any one of the configurations displayed by pressing a key. There is no need to enter any value through the keypad.
The key pad contains four arrow keys (left, right, up and down) 8 Enter, Esc, Alter and Mode keys. The Display key will specify which signals are enabled for display channels. The Reset key resets the system and restores the default values.
Connectors such as phone jacks, I/O BNCs for
feeding-In and observation purposes; "F" type connectors for RF link interfacei D9 connectors for RS232 interfacei power ON switch and universal power socket (lEG) are provided.
The spread spectrum trainer is made up of essential modules already set out herein- The various modules can be used or bypassed depending upon the type of experiment. When these modules are interconnected properly, the spread spectrum trainer will become a ful1 fledge transmitter and receiver of spread spectrum system in the appropriate mode selected. These modules are interconnected using shorting plugs, patch cords and internal logic by selection through the keypad. The user manual suggests the modules to be interconnected for the experiments and furnishes detailed procedure for doing the basic as well as advanced experiments. It also gives description about various possible projects that can be done by the user.
The spread spectrum trainer is constructed with the following facilities to operate for learning,
link / jumper mill be the output of the module or subjection within the module and the other post (called the sinking post) will be the input to the module or the subsection within the module.
The signal will be available in the sourcing post which can be either fed into the sinking post
additional facility of
a)feeding in user generating signal
b)giving out signal to the external circuitry
for the user to analyse and do projects. The
shorting links and jumpers are shown in Fig.7.
Several monitoring posts are available In the
band will be delayed, which is equivalent to travelling in different paths. These delays are user selectable through keypad.
In any real world system the noise becomes one of the unavoidable components by default. The effect of noise will play a major role in the performance of the system• In addition to noise, the jamming signal can also be radiated. The trainer generates various signals like gaussian noise, jamming etc. , to study the effects of them in spread spectrum system. The signal strength is variable by the user to increase or to decrease the effects of noise.
In wireless system the doppler effect is one of the important constituents, This could be in various forms like step, ramp etc. This effect can be simulated in the trainer to show how the tracking takes place at the receiver. The step, ramp inputs etc. are simulated by changing the IF and showing the correlation peak at the receiver.
The trainer operates in several modes depending
upon the module Interconnected and user selection through keypad. The trainer can be operated in base bandy IF, and RF. Operating the trainer at base band and IF allouis to explain and understand the concepts and principles thoroughly and easily.
The trainer has building blocks (modules) for both DS88 and FHSS spread spectrum techniques. It operates in one of the modes based on the selection through keypads. By default, the trainer operates in DSSS.
The trainer uses a microcontroller and a DSP for the entire operation. The DSP does the cor© function at the receiver and the microcontrol1er does the user interface, controls etc. for the trainer. Using DSP gives the advantage of realising the required function® without modification of the trainer- To fully uti1ise this capability for advanced experimentation and analysis, a port is provided in the trainer through which the processor can be accessed. Therefore several functions like code interleaving
etc. can be realised using this facility by changing the subsections of the program. PC can be connected to this port through a PC add-on card and the programs can be downloaded.
Expansion ports for transmitter and receiver is terminated with all required signals to and from the blocks in the trainer including shorting links and Jumpers. These expansion ports are available to interface to the external circuitry for advanced experimentation and projects with the trainer becoming a central platform for such activities. The pin details are available in the user manual.
The incoming signal at the receiver is digitised and fed to the receiver loop for data recovery. This digitised data can be douinloaded to the PC and further processing can be done. Several techniques fol louied in the receiver loop can be implemented using this facility. This allows the trainer to be used as a development platform for the user.
The functioning of the trainer is presented in the form of a block diagram in the front panel as shown in Fig.7 with all user interfaces like shorting links, dumpers, observation posts, i/o posts, potentiometers, keypad, LCD etc. positioned in the appropriate locations in the diagram. This facility gives the -actual picture of the functioning of the entire trainer and therefore the spread spectrum system for the user.
A port for accessing the DSP inside the spread spectrum trainer for advanced experimentation is also made available. The expansion port headers are positioned for easy interface to the external circuitry for prototyping, advanced experimentation and so on.
The spread spectrum trainer will be ideally suited for R & D personnel in Research Labs) undergraduate and graduate students in Electrical/ Electronic and Communication Engineering 9 practising engineers and organisations entering the area of spread spectrum communications; system engineering and system integrators; service providers prototype development centres and so
1. A spread spectrum trainer comprising at least one
transmitter and at least one receiver characterised by a
plurality of interconnected modules adaptable for both DS88 and FH8S techniques, said modules comprising code gien era torsi data generators and decoders; spreaders; frequency synthesizers! BF8K/F8K modulators} multipath simulators! noise source} costas loopi delayed lock loop} and RF transmitter and RF receiver, together with means for altering the module connections and means for configuring the modules for varying the parameters
1, A spread spectrum trainer comprising at lest one/or transmitter and at least one receiver characterised by a plurality of Interconnected module© adaptable for both DS88 and FH8S techniques, said modules comprising code generators; data generators and decoders; spreadersi frequency synthesizers; BP8K/FSK modulators; multipath Simulators; noise source) costas loop) delayed lock loop and RF transmitter and RF receiver, together with means for altering the module connections and means for configuring the modules for varying the parameters
2. A spread spectrum trainer as claimed in Claim 1 wherein the means for altering the module connections comprise means for displaying the input and output of any module; means for connecting I disconnecting, by-passing, substituting, adding-on and building up of a module or modules.
3.A spread spectrum trainer as claimed in Claim 1 or Claim 2 wherein the means for altering module connections comprise phone-Jacks, I/O BNCs, F type and 09 connectors, plugs, patch cords, shorting 1 inks, Jumper posts, monitoring posts, sourcing and sinking posts, input posts, output posts, expansion posts.
4.A spread spectrum trainer as claimed in any one
of the preceding Claims wherein the code
generators comprise means for configuring the same
to various parameters but with common lengths and
means for generating al1 the commonly used code
types (MAXIMAL, GOLD, BARKER and WALSH) and for
giving the epoch (start of sequence) signal output for the data synchronisation.
5. A spread spectrum trainer as claimed in any one of the preceding Claims wherein the means for configuring comprise a display unit and keypad.
6. A spread spectrum trainer as claimed in any one of the preceding Claims wherein the data generator module has an internal generator which generates a square wave form and a PRBS of length 19, the said module also having two codes which can code two audio signals, three RS232 translators and a synchroniser for external data usage•
7. A spread spectrum trainer as claimed in any one of the preceding Claims wherein the decoder comprises means for decoding all the received signals back to the original data.
8. A spread spectrum trainer as claimed in any one of the preceding Claims wherein each spreader has means for modulating the generated code over data, the outputs of the spreader going back to BPSK modulator or multipath mimulator through jumper
9. A spread spectrum trainer as claimed in any one of the preceding Claims wherein the frequency synthesizer is of the direct digital frequency type (DDF8) driven by a crystal osci1 lator and control1ed by a microcontroller, said synthesizer generating all the necessary locks and carrying out FSK modulation.
10. A spread spectrum trainer as claimed in any one of the preceding Claims wherein the BPSK modulator consists of double balanced mixers which modulates the IF carrier with the spread data, the output of the modulators being summed linearly to set the composite CDMA signals.
11. A spread spectrum trainer as claimed in any one of the precedTng Claims wherein the multipath simulator module has means for introducing fixed delays in spread data.
12. A spread spectrum trainer as claimed in any
one of the preceding Claims wherein the means for
varying the strength of the signal comprise a
13. A spread spectrum trainer as claimed in any one of the preceding Claims wherein the noise source comprises means for generating a single tone jamming noise at IF, a Gaussian noise at base band and a Gaussian noise at IF together with means for selecting any one of the noises and adding it on to the received signal.
14. A spread spectrum trainer as claimed in any one of the preceding Claims wherein the costas loop is digitally implemented and comprises means for programming the loop parameters-
15- A spread spectrum trainer as claimed in any one of the preceding Claims wherein the delay locked loop has means for tracking the code that is used for spreading.
16. A spread spectrum trainer as claimed in any one of the preceding Claims wherein the transmitter comprises means for generating hopping frequenclesi making use of DDFS, a code generator control 1ing the hopping pattern.
17. A spread spectrum trainer as claimed in any
one of the preceding Claims wherein the receiver is digitally implemented.
IS. A ttpread SSSpectrum trainer as claimed in any one of the preceding Claims wherein, the R-f transmitter comprises has means for converting IF signal to RF in ISM band and also comprises a radio frequency VCO, Up converter, power amplifier and an antenna.
19. A spread spectrum trainer as claimed in any one of the preceding Claims wherein the RF receiver comprises means to convert the RF back to IF and also comprises a down converter, BPF and LPF and an antenna.
20. A spread spectrum trainer as claimed In any one of the preceding Claims wherein a LCD display panel, 10 element BAR LEDs and key pad are provided for configuring.
21. A spread spectrum trainer as claimed In any one of the preceding Claims wherein the key pad contains four arrow keys (left, right, up and down); Enter; Esc; Alter; Mode keys; Display key; and a Reset key.
22. A spread spectrum trainer as claimed in any one of the preceding Claims wherein are provided connectors such as phone jacks, I/O BNCs for feeding-in and observation purposes; "F" type connectors for RF link interface; D9 connectors for RS232 interface, power ON switch and universal power socket (lEC).
23- A spread spectrum trainer as claimed in any one of the preceding Claims wherein is provided a port for accessing the DSP.
24. A spread spectrum trainer substantially as herein described with reference to, and as illustrated in, the accompanying drawings-
|Indian Patent Application Number||1996/MAS/1998|
|PG Journal Number||27/2007|
|Date of Filing||04-Sep-1998|
|Name of Patentee||BENCHMARK ELECTRONIC SYSTEMS (P)LIMITED|
|Applicant Address||PLOT NO.58,ELECTRICAL, PERUNGUDI ,CHENNAI 600 096.|
|PCT International Classification Number||H04J13/02|
|PCT International Application Number||N/A|
|PCT International Filing date|