EP1230786A1

EP1230786A1 - Wireless modem

Info

Publication number: EP1230786A1
Application number: EP00974036A
Authority: EP
Inventors: Prapan Paul Tinaphong; Thongchai 99/209 Pruksachart 15 PRANGTIP
Original assignee: Thomson Licensing SAS
Priority date: 1999-10-29
Filing date: 2000-10-30
Publication date: 2002-08-14
Also published as: WO2001033824A1; CN1385027A; KR20020044575A; AU1246901A; JP2003535489A; CN1241432C

Abstract

A wireless modem system having two devices, wherein each device can transmit and receive data via a plurality of RF channels, the data being applied to the channels in sequence. In one embodiment, a first device may be used for coupling to a computer for receiving data from the computer. The first device encodes the received data from the computer and transmits the received data using a digital wireless transmission format to a second device. The second device receives the transmitted data from the first device in the digital wireless transmission format and further processing it into an analog format for transmission over a wired telephone network.

Description

WIRELESS MODEM

FIELD OF THE INVENTION

The present invention relates to wireless communication, and more

particularly to a wireless modem system which allows a computer to process data

remotely, without physically being tied to a telephone phone port. The system

operates in such manner as to protect the integrity of the communications sent

and/ or received over such modem.

BACKGROUND OF THE INVENTION

Modems are widely used throughout the world to enable electronic devices

such as computers to communicate with one another. Typically, modems couple a

computer to a communications jack through which communications can be sent

and/ or received by means of a wire or a cable. However, requiring that a modem be

physically coupled to a jack limits the ability to move freely while using modem-

enabled devices. In response, wireless modems have been designed to enable users to

send and/ or receive communications from laptop computers and other electronic

devices without the computer having to be physically connected to a jack thereby

enabling the computer to be used for communications irrespective of its location with

respect to a jack. However, conventional wireless modems suffer form a significant

drawback. Specifically, the integrity of communications sent and/ or received using

such devices often fails. Accordingly, it is an object of the present invention to

provide a wireless modem that provides greater communications integrity. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of an exemplary embodiment of the present

wireless modem system according to the present invention.

FIG. 2 shows a flowchart of the power-up initialization for the devices shown

in FIG. 1.

FIG. 3 shows a flowchart for a continuously running loop, RL, that executes

alignment bit monitoring and received data buffer monitor receives in the devices

shown in FIG. 1.

FIG. 4 shows a flowchart for data transmission by the devices shown in FIG. I.

FIG. 5 shows a flowchart for U ART/ modem interrupt handling by the devices

shown in FIG. 1.

FIG. 6 shows a flowchart for data reception by the devices shown in FIG. 1.

FIG. 7 shows a flowchart for no packet received channel tracking timer

interrupt by the devices shown in FIG. 1.

FIG. 8 shows a schematic diagram of a main processor used in the devices

shown in FIG. 1 and includes an SST (Spread Spectrum Technology) processor and a

SRAM for the devices shown in FIG. 1.

FIG. 9 shows a schematic diagram of the UART, the led indicator and an RS-

232 interface used in the devices shown in FIG. 1.

FIG. 10 shows a schematic diagram of the RF transceiver used in the devices

shown in FIG. 1. FIG. 11 shows a schematic diagram of a power supply used in the devices

shown in FIG. 1.

FIGS. 12 and 13 show a circuit diagram of the devices shown in FIG. 1.

SUMMARY

In accordance with the present invention, a wireless modem system that

preserves the integrity of communications using digital spread spectrum operation

providing automatic RF signal detection so as to lock on the selected channel after a

handshake process. In particular, the modem function for modulating and

demodulating the data to and from the computer for transmitting over an analog

telephone line resides only in the remote wireless modem.

DETAILED DESCRIPTION OF THE INVENTION

Wireless modem (WM) devices used for the Wireless modem system

described herein and also referred to as a wireless modem jack (WMJ) or an RF link

will operate, for example, in the 900 MHz ISM band (902 - 928 MHz). The wireless

modem system comprises one base unit 1000 and one wireless remote modem unit

10001, shown for example, in Fig. 1. Both units will be able to transmit and receive

data/ fax at the same time. The only difference is that the base unit 1000 does not

need a "modem" function (e.g., 18') and the associated telephony processing (e.g.,

20'), since the data are being modulated and demodulated into an analog signal to be

transmitted and received at the remote wireless unit 1001, as shown in Fig. 1.

The design of the system is based preferably on the Direct Sequence Spread

Spectrum (DSSS) technology, which also provides a maximum security for the data

transmission over the Radio Frequency spectrum, especially in the 900 MHz range. At the present time, the maximum data transmission rate for the WMJ will be up to

115 Kbps (via Radio Frequency link), which is a much higher speed when compared

to a regular hard-wired modem connection. The WMJ can be used for Internet

service connection, as well as sending/ receiving fax data and for communicating

other forms of data. All transmission is in the SST digital encryption format.

Hence, the present invention allows RF link supports of up to 115 kbps data

rate with error detection and correction. It is compatible with V.90/56K flex modem

standard, which allows it to be used for many existing Internet Service Provider

services. The system provides automatic RF signal detection and locks into the

selected channel for both units (after an identified hand shake process), as described

below.

Since Base unit 1000 consists of a serial port, the system can be used not only

as a traditional modem to access a computer network through the telephone line, but

can also be used for remote printer sharing, network connection between two PC

terminals. The system may also support Hyper Terminal data transmission.

In addition, since the modulation signal is in the digital format, therefore, FCC

allows the maximum transmission power up to one (1) watt, instead of 100 mW as in

the Analog modulation type. This will allow for the better range of transmission,

normally it will go up to 300 ft range (or better) in the residential environmental

condition.

Nowadays, the Personal Computer (PC) and Internet are very popular

through out the world. Most consumers can access the Internet by using a normal

connection through a regular telephone jack. Unfortunately, most residential homes have only one or two telephone wall-jacks throughout the house. Therefore, it is a

problem for most people to set up a PC in a location that is far from a telephone

wall-jack.

Using the WMJ, a consumer can, for example, access the Internet, or

send/ receive fax, or transfer files between two PCs from everywhere throughout a

house. The data (signal) will be in the Digital format with signal encryption. The

Radio Frequency (RF) signal will be in the 900 MHz range; from 902 - 928 MHz. The

WMJ design is based on the Digital Spread Spectrum technology. Therefore, the WMJ

can transmit and receive a signal over greater distances (approximately 300 feet) than

any 900 MHz device that transmits the signal in a regular Analog modulation format.

Part 15 of FCC regulations allows any device with Digital Modulation format to have

RF output power of I W, compared to a device with Analog Modulation format

which is allowed to have output power of 100 mW only.

Reference is made to the block diagram of FIG. 1 for a base unit RF link. The

overall operation will first be described for a situation in which the RF link is

transmitting data from a PC, not shown, and then for a situation in which the RF link

is receiving data from an RF link transmitter, not shown. It is noted here again that

the only difference between a base unit 1000 and a remote unit or extension 1001 is

that a remote unit has additionally a modem function 18' built in and additional

circuit 20' for interfacing to an RJ-11 jack to a telephone network. Therefore, to avoid

redundancy, the following description will concentrate mainly on the base unit.

A DCE port 2 is coupled to the PC computer, not shown and conveys the

serial digital data received to an interface 4 that adjusts the voltage level of the bits to a standard value. A UART 6 translates the serial data into parallel data and a

processor 14 constructs a data packet having an alignment bit, a lead byte, message

bytes and a trailing byte. The packet is then stored in a Tx buffer in a SRAM 8. An

SST 10 looks for unused channels in an RF module 12, reads the data from the Tx

buffer in the SRAM 8 and supplies the data to the channels of the RF module 12 in

repeated sequence. All actions are controlled by an MCU 14 and LED indicators 16

indicate various operating conditions.

When the RF link of FIG. 1 is to receive data from an exterior RF links, the SST

scans the channels of the module 12, and data received therefrom is transferred by

the SST to an Rx buffer, not shown in the SRAM 8. Under control of the MCU 14, the

data in the data packet is reconstructed and conveyed to the UART 6 where the

parallel data is translated into a serial stream of bits that are adjusted in voltage at the

interface 4 before being applied to the DCE port 2 that may be coupled to another PC.

Initialization

Attention is now drawn to the flowchart of FIG. 2 illustrating what occurs at

either a base unit or an extension unit when power is turned on as indicated at 22. If a

test at the unit's SRAM 8 indicates it is defective, nothing more occurs for without a

properly operating SRAM 8 no operation can be carried out. At diamond-shaped

decision block (hereinafter "decision block") 26 it is determined whether something is

coupled to the DCE port 2. If something is so coupled, a PC for example, and if it is a

base unit, BU, as shown in FIG. 1, the modem 18 is ignored and the BU must be set as

a master slave as indicated at 28. The master bit of DIPSW 1 shown in FIG. 8 is tested.

If this switch is on (or set in 'up' position), a corresponding master bit of OPSTAT (operating status) register is set. Otherwise the bit is cleared. Normally an extension

unit (EU) is always set as master unit (the one that initiates transmission) and the

Base Unit (BU) is set as slave unit (the one that is always in listening mode). For

applications that do not need modem function, two BUs may be used. In such case,

one BU must be set as 'master' and the other is set as 'slave'. If required, BU (with

serial port selected) may also be set as master while another BU (with serial port

selected), or extension unit EU is set as a slave.

If, as indicated at a decision block 30, a master setting has been made, the

channels of the RF module 12 are scanned as indicated at 32. The master unit

monitors RSSI (Receive Signal Strength Indicator) of individual RF channel for

100ms. All of ten RF channels (0-9) are scanned. The most quiescent channel is then

selected. Afterward, master unit monitors if there is any transmission activity on the

channel. If not, the channel is selected for transmission. A timer of MCU 14 is used

for a channel scan timer which is handled by a chscan_to interrupt service routine.

After a channel is selected, the no packet received timer is actuated as

indicated at 34. This is to force itself to enter link setup procedure upon the timer

expiration. The procedure of FIG. 7 is then followed. Then, at 36 the appropriate

register of the Rx buffers and the HDx (transmit or receive mode of operation) is set.

At this point the unit enters a runtime loop RL shown in FIG. 3. Referring to decision block 30, if the unit is not set as a master and is therefore

a slave, it will then set the UART 6 baud rate at 38 and start the tracking timer at 40.

This function is only carried out in a slave unit and consists of scanning the RF

channels of a master unit. By way of example, each channel is scanned for 20

milliseconds.

Referring to decision block 26, if the DTR is not active, a check is made at 42 to

see if modem 18 is installed. If it is, the unit is set as a slave and enable modem Rx

interrupt at 44 meaning that no communication is to be made with the modem and

proceed to the block 36. If it is not, a slave enable UART Rx interrupt is set at 46 and

routine returns to the block 28.

Runtime Loop

After the setup routine has been accomplished in FIG. 2, the radio links enter a

continuously operating runtime loop shown in FIG. 3. At decision block 48, a query is

made as to whether or not an alignment byte has been received. Since there is no

alignment byte at the end of a data packet, its absence means that the data packet has

been received. If it has been received, an RBUF in service routine is entered in which

data is stored in the Tx buffer or in the Rx buffer in the SRAM 8. This small loop is

repeated until no alignment byte is received . If there is no indication of an

alignment byte at 48, a check is made at 50 to see if an RF link has been declared up,

meaning that a handshake has been completed so that the RF link is ready for

transmission of data. If not, there is no use in proceeding and the procedure goes

back to the start of the loop. But if an RF link has been declared up at 50, a

determination is made at 52 as to whether there is any data in the Rx data buffer in the SRAM 8. If there is, it is sent to the UART 6 or to the modem 18 indicated at 54

depending upon which type of operation is to take place. The unit forwards data

from the receiver buffer to the UART 6 or modem 18 for the base unit BU only if both

DTR is active (e.g. PC connecting to the port is not ready), and the link is in 'up'

condition. The modem function is relevant to only the BU. Writing/ reading to/ from

UART 6 or the modem corresponds to writing/ reading to/ from UART 6 or the

modem's FIFO buffer. After data is sent, procedure returns to the beginning of the

loop.

Transmission

Data transmission is carried out as indicated in FIG. 4 starting at 56. First, any

data in the TX buffer in the SRAM 8 is transmitted. A check is first made at 58 as to

whether a resent bit has been received from block 118 shown in FIG. 7 which is a

request that a transmission be repeated. If so, the pointer in the TX buffer in the

SRAM 8 is restored at 60, but if not, the data is read from the Tx data buffer at 62. The

Tx buffer pointer is saved at 64, and the data packet is constructed in the UART 6 as

indicated at 66. Data is copied from transmit buffer of the SRAM 8 to the data portion

of the packet buffer (MCU's registers). The number of bytes in a data packet is 0 (nil)

to 72. A packet envelope is added. The envelope comprises packet header byte, link

control byte, packet length (counted from header byte to last byte of checksum), and

channel number/ unit i.d. byte.

At 68, the routine calculates and appends 16-bit fletcher checksum at the end

of the last data byte. A transmitted packet is preceded by 15 preamble bytes (0x00) and 2 alignment bytes (0x80). Five trailing bytes (Oxff) are appended at the end of

packet transmission.

At 70, a check is made as to whether or not the RF link is set by a manual

switch as a master unit. If it is, the no packet received timer is started at 72 and the

procedure shown in FIG. 7 and to be described is followed.

FIG. 5 shows a flowchart depicting the steps for UART/ Modem Interrupt

Handling Service 102 in which data is read from either the UART 6 or the modem Rx

FIFO at 104. Until buffer is empty and then written into the Tx data buffer at 106 and

returned at 108 to the start of transmission 56 of FIG 4.

Reception

Referring to FIG. 6 starting at 74, the routine monitors for two consecutive

alignment bytes (0x80). These bytes may not be properly aligned. The unit reads and

aligns next seven bytes of data in the packet (6 to 78). If the packet length exceeds 6

(but not more than 78), the unit reads remaining bytes from SST and stores in packet

buffer (MCU's register). If a header byte is received, decision block 76, the data is

read from the SST Rx FIFO in the SRAM 8 as indicated at 78. At decision block 80, the

data packet's validity is checked. At decision block 82, a check is made of the data to

see if its address is that of the receiving RF link. This is a program function in the

MCV8 of both units for checking to see whether the link up or link down for the

packet has been set so as to prepare the master and slave units for transmission. This

prevents picking up a neighbor's transmission. The link is declared up at block 84 by

a light indicating the RF link is ready to receive and a check is made at 86 to see if the

master/ slave switch is set at the slave position. If so, the user may set the baud rate at 88 with a combination of switches or via software. Usually the baud rate is set at a

maximum. The no packet received timer is started at 90, see FIG. 7, and at 92 a link

setup packet is set up in MCU 14 to ask for more data from the buffer. If decision

block 86 indicates it is a master, data is sent at a block 87 and the runtime loop of FIG.

3 is entered.

Referring again to decision block 82, when a link setup packet indicates as not

being received. If at 94, the data packet has been received in sequence, it is written

into the Rx data buffer on the SRAM 8 and sent to 100. A NO indication from any of

the decision blocks 76, 80 and 94 causes the procedure to go back to the runtime loop

of FIG. 3.

FIG. 7 illustrates for both masters and slaves the No Packet Received/ Channel

Tracking Timer Interrupt Handling routines. If two data links are up as determined

at decision block 110, i.e., if there has been a handshake between them, a time out

counter is read at 112. A time out counter starts counting if there is an interruption of

transmission. As each data packet is transmitted, the time out counter starts running

and when the last or trailer byte of a message has been passed, the clock is set back to

0. Therefore, if at decision block 114, the counter is not 0, it means that the data

packet was not completely transmitted, in which event a resent bit is sent back to the

transmitter. This is the reset bit referred to at decision block 58 in FIG. 4 that

illustrates transmission. After this is done, the procedure returns to decision block

110.

A time-out counter is maintained and used by both the master and slave units

to declare link down. The value of the counter is different for the master and slave units, i.e., 10 and 1 for the master and slave, respectively. Furthermore, the value of

the NPR (No-packet received) timer is different for the master and slave units, i.e.,

50ms and 1000ms for the master and slave, respectively.

For the master unit, if no valid data packet is received from the slave unit

within 50ms after sending a data packet, the master unit re-transmits the data packet.

Ten successive expirations of the NPR timer declares the link down, and the master

unit re-enters the channel scan process. The counter is re-loaded each time a valid

data packet is received. The value of the NPR should be sufficient to cope with the

longest data packet. The data packet length varies from 6 to 78 bytes, excluding the

preamble, alignment and trailing bits.

Since the slave unit is always in listening mode, i.e., never initiates data packet

transmission, only one time of the NPR expiration is sufficient to declare link down.

The value of the NPR is chosen to cover the total time the master unit attempts to

receive responses from the slave unit by re-transmitting data a packet, i.e., 10 x 50ms.

After declaring link down, the slave unit "plays dead" for another 1000ms to ensure

that the master unit has declared link down and re-initiated link set-up. Note that the

foregoing mechanism is not used during the link setup process since the master unit

will continually send link setup so long as there is no response received from the

slave unit.

If, however, it is indicated at decision block 114 that the time out counter has

gone back to 0, it is the end of the transmission for the master and slave units, but

they will stay in the handshake mode until a determination is made at decision block 116 whether this is a master or slave. If it is a master, the SST 10 scans channels at 117

as indicated at the blocks 32 and 34 of FIG. 2.

On the other hand, if decision block 116 indicates that the RF link is not a

master, and therefore is a slave, the master, at block 126, then is told to declare the

link down, i.e., to declare the end of the transmission for the master and slave units,

but they remain in the handshake mode. At 128, available channels are found. These

are used in the DSS mode at a block 124 in which a tracking timer is started so as to

send data in the available channels in sequence.

If the indication at decision block 110 is that the link between the RF units has

not been properly established, i.e., the link is not up. If at decision block 120 it is

determined that it is not a master unit, i.e., it is a slave, a block 122 finds available

channels in the same way as the block 124. If the indication at decision block 120 is

that it is a master unit, a data packet is sent at a block 126 and a no packet received

timer is started at a block 128.

In discussing the schematic diagrams of FIGS. 8-13, it is to be understood that

the particular microchips designated are only exemplary of what can be used. They

will be designated by their "U" number and their acronyms.

FIG. 8 is a schematic diagram of the main processor in which the MCU 140 is

U . Patterns for testing the SRAM 8, U₆, as at the block 24 of FIG. 2 and the replies of

the SRAM, U₆ are conveyed by data path 130. Switches for providing the RF link

identification , the baud rate and whether a unit is a master or a slave are indicated at

132 and are coupled via a buffer 134 and data path 136 to the pins 138 on the MCU,

U . An oscillator 138 provides RF to the SST chip 141 to the GFSK transceiver 142 of FIG. 10 via a lead 144, and it provides ten RF channels to an antenna 145 of FIG. 10.

No attempt has been made to describe every connection because it is believed that

one skilled in the art would know from what is shown and described how to practice

the invention.

FIG. 9 is a schematic diagram showing the UART 6 as U_o and the RS-232

interface processing 4 at 146. The DCE com port 2 is indicated by 148 and the LEDs

for indicating various operating conditions are indicated at 150.

FIG. 11 is a schematic diagram showing a power supply 152 for use with a

base unit such as shown in FIG. 1 and a power supply 154 for an extension unit.

FIGS. 12 and 13 are schematic diagrams for the modem 18 that permits an

extension unit to communicate with the Internet. It is comprised of U ₈ and Uis, and

has a jack 154 for coupling to a phone line.

Numerous modifications to and alternative embodiments of the present

invention will be apparent to those skilled in the art in view of the foregoing

description. Accordingly, this description is to be construed as illustrative only and

is for the purpose of teaching those skilled in the art the best mode of carrying out

the invention. Details of the embodiment may be varied without departing from the

spirit of the invention, and the exclusive use of all modifications which come within

the scope of the appended claims is reserved.

Claims

1. A wireless modem system, comprising a first and a second device, wherein:

the first device comprising

means for coupling to a computer for receiving data from said computer;

means for encoding the received data and transmitting the received data using

a digital wireless transmission format; and

the second device comprising

means for receiving the transmitted data from the first device in the digital

wireless transmission format and further processing it into an analog format for

transmission over a wired telephone network.

2. The system of claim 1 wherein the received data is transmitted to the second

device using the digital wireless transmission format in a selected one of available

channels.

3. The system of claim 1 wherein the second device comprises a modem for

the further processing the received transmitted data into the analog format.

4. The system of claim 3 wherein the modem receives and demodulates an

analog signal from the wired telephone network.

5. A wireless modem system comprising first and second devices, each of said

devices having:

a port for receiving series data;

signal translation means for translating serial data applied to either side

thereof into parallel data coupled to said port;

a transmitter buffer;

a receiver buffer;

control means for creating data packets from data emerging from said signal

translation means;

means for coupling said data packets to said transmitter buffer;

a transceiver having a plurality of channels;

means for applying data in said transmitter buffer to selected channels of said

transceiver in repeated sequence; and

means for storing data packets received by said transceiver in said receiver

buffer, said control means being adapted to transfer the packets in said receiver

buffer to said signal translation means.

6. The modem according to Claim 5, further comprising means for

scanning the channels of said transceiver to identify clear channels, said channels

being used as said selected channels.

7. The modem according to Claim 4, further comprising:

manually controlled means in each one of said first and second devices for

selectively establishing its address;

manually controlled means in each one of said first and second devices for

establishing the address of the other RF device;

means in said first and second devices for writing its address and the address

of the other devices into its transmitter buffer;

means in said first and second devices responsive to the reception of its owri

address for comparing a received address for the other device with the known

address for the other RF device; and

means for carrying on further communications if the compared addresses are

the same.