WO2004075430A1

WO2004075430A1 - Demodulation method in wireless telemetry systems using frame combining

Info

Publication number: WO2004075430A1
Application number: PCT/KR2003/000365
Authority: WO
Inventors: Jae-Seok Kim; Gun-Hee Han; Seong-Joo Lee
Original assignee: Yonsei University
Priority date: 2003-02-18
Filing date: 2003-02-24
Publication date: 2004-09-02
Also published as: KR20040074412A; AU2003217501A1; KR100522883B1

Abstract

Disclosed herein is a demodulation method in wireless telemetry systems using frame combining. In detail, this invention is related to the CDMA wireless communication systems, especially a demodulation method by frame combining method which uses time diversity in a wireless measuring instrument that is used for wireless telemetry systems. In transmission data of the present invention, CU(Control Unit) transmits the same frame repeatedly several times and RT(Remote Terminal) combines the transmitted frame, which improve signal-to-noise ratio of signal that is demodulated. Therefore, according to the present invention, there is effect that can minimize RT’s hardware complexity and reduce electric power consumption, and reduce production costs of modem.

Description

DEMODULATION METHOD IN WIRELESS TELEMETRY SYSTEMS USING

FRAME COMBINING

Technical Field

The present invention relates to a demodulation method in wireless telemetry

systems using frame combining. More specifically, the invention relates to a

demodulation method by frame combining which uses time diversity in CDMA wireless

communication systems, especially, in a remote terminal (hereinafter, referred to as

"RT") that is used for wireless telemetry systems.

Background Art

Code division multiple access (CDMA) employs a demodulation method in which

a rake receiver divides signals transmitted through multiple paths, demodulates them,

and then combines the demodulated signals, to improve signal-to-noise ratio. However,

the rake receiver must have a plurality of independent modulators in order to divide the

signals transmitted through the multiple paths. This increases hardware complexity of

the receiver. The rake receiver structure can be an appropriate method for improving the

performance of a modem used for high-quality audio and data communication, such as

those used in mobile communication systems. However, it is impossible to employ the

rake receiver structure in RTs that require to be constructed at a low cost and carry out

only low-speed data transmission with low power.

FIG. 1 shows utilization of the rake receiver in a conventional CDMA system. The rake receiver operates in such a manner that each of m independent CDMA

demodulators 2 accepts received signals 1, separate the signals transmitted through

multiple paths into one another, and demodulate the separated signals by paths. A

symbol combiner 3 combines the demodulated symbols modulated by the CDMA

demodulators to finally output a demodulated symbol 4. As shown in FIG. 1, as the

number of the CDMA demodulators increases, hardware complexity also increases while

signal-to-noise ratio is improved. This is not suitable for RTs that must have minimized

hardware complexity.

Disclosure of Invention

Accordingly, the present invention has been made in view of the above problems,

and it is an object of the present invention is to provide a demodulation method in

wireless telemetry systems, which employs frame combining using time diversity, to

remarkably reduce hardware complexity of a modem used for RTs. The demodulation

method using frame combining according to the present invention can solve problems

with respect to hardware complexity of the modem, which are generated where the rake

receiver structure is used in the modem when signals are transmitted by CDMA in

wireless telemetry systems,

To accomplish the above object,- in wireless telemetry systems, a control unit

(hereinafter, referred to as "CU") transmits the same frame repeatedly several times and

RT combines the transmitted frame, which improve signal-to-noise ratio of a

demodulated signal. Brief Description of the Drawings

Further objects and advantages of the invention can be more fully understood from

the following detailed description taken in conjunction with the accompanying drawings,

in which:

FIG. 1 shows utilization of a rake receiver in a conventional CDMA system;

FIG. 2 shows a data transmission method in which CU transmits data to a plurality

of distributed RTS using one pilot channel and a plurality of data channels;

FIG. 3 shows the construction of a receiver that employs a demodulation method

according to the present invention;

FIG. 4 shows application of the demodulation method according to the present

invention to a receiver structure using a plurality of demodulators;

FIG. 5 shows a frame combining method that is carried out in the receiver

employing the demodulation method according to the present invention; and

FIG. 6 is a graph showing comparison of frame error rates of the demodulation

method of the present invention and conventional method in Rayleigh fading channel

environment.

Best Mode for Carrying Out the Invention

The present invention will now be described in detail in connection with preferred

embodiments with reference to the accompanying drawings.

of distributed RTS using one pilot channel and a plurality of data channels. CU transmits a pilot channel 5 for PN code synchronization and demodulation of synchronous signals.

If required, CU can deliver a plurality of data channels 6 and 7. The data channels 6 and

7 are spread in orthogonal codes for channel division and transmitted. In the case that the

period of each of the data channel 6 and 7 corresponds to 1/N of the period of the pilot

channel 5, CU transmits each data channel repeatedly N times so that the frame start

point of the pilot channel 5 coincides with the frame start point of each data channel. In

case of the data channel i 6, for instance, its frame period is 1/m of the frame period of

the pilot channel 5. Thus, CU repeatedly transmits the data channel 6 m times. In case of

the data channel j 7, CU repeatedly transmits it k times because its frame period

corresponds to 1 k of that of the pilot channel.

RT recognizes the frame start point of the pilot channel when PN code

synchronization is achieved through the pilot channel. RT can automatically recognize

the frame start point of each data channel because the frame start point of the pilot

channel coincides with that of the data channel. RT combines the repeatedly transmitted

frame in terms of time according to a predetermined agreement, considering how many

times a data frame is repeatedly transmitted for one pilot channel.

FIG. 3 shows the construction of a receiver that employs the demodulation method

according to the present invention.

In case of utilizing the demodulation method according to the present invention,

the rake receiver structure is not necessarily used for the purpose of improving signal-to-

noise ratio. In the receiver according to the present invention, as shown in FIG. 3, a

single CDMA demodulator 9 accepts received signals 8 and demodulates frame data that is repeatedly transmitted to send the demodulated frame data to a frame combiner 10.

The frame combiner 10 accumulates the frame data demodulated by the demodulator 9

by a predetermined number of repeating times and then outputs final combined data 11.

FIG. 4 shows a receiver structure using a plurality of demodulators to which the

demodulation method according to the present invention is applied.

In the case that signal variation is severe in multi-path fading channel

environments, even the demodulation method of the present invention may use a

plurality of CDMA demodulators in order to improve reliability in demodulation. While

the conventional demodulation method combines all signals demodulated by m CDMA

demodulators, the demodulation method of the present invention selects only the CDMA

demodulator that has the maximum energy value from m CDMA demodulators for every

frame and transmits data demodulated by the selected demodulator to a frame combiner.

Specifically, each of m CDMA demodulators 13 accepts received signals 12. Energy

values of signals outputted from the m CDMA demodulators are compared to select only

the demodulator that has the maximum energy value (14), and data outputted from the

selected demodulator is transmitted to the frame combiner 15. The frame combiner 15

combines frame data repeatedly transmitted and finally outputs a demodulated symbol

16.

FIG. 5 shows a frame combining method that is executed in the receiver that

employs the demodulation method according to the present invention. If a frame

transmitted is N bits, the frame combiner must have N registers 17. When a CDMA

demodulator demodulates the first frame and transmits the demodulated frame to the frame combiner, the frame combiner stores the data of the demodulated frame in N

registers 17. Here, the stored N data items Cy correspond to symbol data items that were

demodulated when the first frame was demodulated.

Next, the demodulator demodulates the second frame and sends the demodulated

frame to the frame combiner. Then, the frame combiner adds the symbol data of the

transmitted frame to the N symbol data items previously stored and stores the added

symbol data. Accordingly, N data items C_2j stored in the frame combiner after

demodulation of the second frame correspond to the sum of the symbol data of the first

frame and the symbol data obtained when the second frame is demodulated.

If a frame is transmitted repeatedly m times, the CDMA demodulator demodulates

m frames and transmits the demodulated frames to the frame combiner. Upon

completion of demodulation of the mth frame, the frame combiner combines the m

frames and finally outputs N symbol data items C_mj. The final data items C_mj

correspond to the sum of the repeatedly transmitted symbol data items from the first

frame to the mth frame.

When the mth frame is demodulated and then combining of all frames is finished,

the frame combiner outputs the final data and initializes the registers for combining new

frames transmitted thereto.

FIG. 6 is a graph showing comparison of frame error rates of the demodulation

environment.

In case of a conventional algorithm 18 that transmits a frame only once to demodulate it, its performance is very poor in terms of frame error rate when the rake

receiver is not used, as shown in FIG. 6. Frame error rate reaches 60% approximately

even when signal-to-noise ratio is increased to lOdB. However, algorithms of repeatedly

transmitting a frame and combining the frame to demodulate it, proposed by the present

invention, has performance much superior to the conventional algorithm. In case of an

algorithm 19 that repeatedly transmits a frame twice, it can be known from FIG. 6 that

frame error rate is reduced to 10% when signal-to-noise ratio is increased to lOdB. An

increase in the number of times of repeating the frame brings about higher performance.

In case of an algorithm 20 that repeatedly transmits a frames four times, frame error rate

is decreased to 1% when signal-to-noise ratio is increased to only 7dB.

As described above, the frame combining technique using time diversity according

to the present invention can improve signal-to-noise ratio even when the rake receiver is

not used in the receiver modem, distinguished from the conventional CDMA system

demodulation method, which can reduce hardware complexity of the modem. Especially,

the present invention is very effective for a modem used for RT that is very small and

requires low-power operation in wireless telemetry systems.

While the present invention has been described with reference to the particular

illustrative embodiments, it is not to be restricted by the embodiments but only by the

appended claims. It is to be appreciated that those skilled in the art can change or modify

the embodiments without departing from the scope and spirit of the present invention.

As described above, according to the demodulation method in wireless telemetry

systems using frame combining according to the present invention, the receiver does not employ the rake receiver structure so that hardware complexity of RT is minimized and

power consumption is reduced. Furthermore, production costs of the modem is

remarkably decreased. The present invention especially effective in wireless telemetry

systems that should provide and accept a large number of RTs at a low price.

Claims

What Is Claimed Is:

1. A demodulation method in wireless telemetry systems using frame combining,

in which a control unit transmits frame data repeatedly and a receiver of a remote

terminal combines the repeatedly transmitted frame.

2. The demodulation method as claimed in claim 1, wherein the remote terminal

uses only one CDMA demodulator, and a frame combiner combines the repeatedly

transmitted frame.

3. The demodulation method as claimed in claim 1, wherein the remote terminal

uses a plurality of CDMA demodulators, selects only the demodulator that has the

maximum energy from the plurality of demodulators for every frame and transmits

symbols of the frame demodulated by the selected demodulator to a frame combiner, and

the frame combiner combines the repeatedly transmitted frame.

4. The demodulation method as claimed in claim 2 or 3, wherein the frame

combiner has registers as many as the number of symbols of the transmitted frame, and

combines the transmitted frame in such a manner that it accumulates the repeatedly

transmitted frame in each register.

5. The demodulation method as claimed in any one of claims 1 to 3, wherein the control unit transmits one pilot channel and a plurality of data channels, makes the frame

length of each data channel identical to 1/N of that of the pilot channel, and repeats each

data frame N times so that the frame start point of the pilot channel coincides with the

frame start point of each data channel.

6. The demodulation method as claimed in claim 5, wherein the frame start point

of each data channel must coincide with the frame start point of the pilot channel all the

time irrespective of the frame length of each data channel transmitted by the control unit.

7 The demodulation method as claimed in claim 1 or 2, comprising:

a first step in which the remote terminal performs PN' code synchronization using the

pilot channel received from the control unit;

a second step in which the remote terminal judges the frame start point of the pilot

channel to start demodulation of a data channel transmitted at that point;

a third step in which the remote terminal demodulates data for a predetermined frame

length, and then stores the demodulated data in the frame combiner;

a fourth step in which the remote terminal accumulates demodulated data of a data

chamiel repeatedly transmitted until a next pilot channel starts in the frame combiner and,

combining is finished, outputs final data and initializes internal registers of the frame

combiner; and

a fifth step of repeatedly performing the second, third and fourth steps.

8. The demodulation method as claimed in claim 1 or 3, comprising:

a first step in which each of m CDMA demodulators of the remote terminal

independently performs PN code synchronization using the pilot channel received from

the control unit;

a second step in which each of the m CDMA demodulators of the remote terminal

independently judges the frame start point of the pilot channel to start demodulation of a

data channel transmitted at that point;

a third step of selecting the demodulator having the maximum energy from the m

CDMA demodulators of the remote terminal;

a fourth step in which the selected demodulator demodulates data for a predetermined

frame length and then stores the demodulated data in the frame combiner;

a fifth step in which the remote terminal repeatedly performs the third and fourth steps

for every frame, accumulates demodulated data of a data channel repeatedly transmitted

until a next pilot channel starts in the frame combiner and, combining is finished,

outputs final data and initializes internal registers of the frame combiner; and

a sixth step of repeatedly performing the second to fifth steps.