CN1241432C - wireless modem - Google Patents

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

technical field

The present invention relates to wireless communications, and more particularly, the present invention relates to a wireless modem system that allows a computer to process data remotely without being physically dependent on a telephone handset communication port. The system operates to protect the integrity of communications sent and/or received on such modems.

Background technique

Modems are used throughout the world to enable electronic devices, such as computers, to communicate with each other. Modems typically couple a computer to a communications jack through which communications are sent and/or received using a wire or cable. However, requiring a modem to be physically coupled to a jack limits the ability to move freely while using the modem-enabled device. In response, wireless modems were designed to enable users to send and/or receive communications from laptop computers and other electronic devices without requiring the computer to be physically connected to a jack, thereby enabling the computer to be used regardless of its A jack location for communications. However, traditional wireless modems have a serious drawback. Specifically, the integrity of communications sent and/or received using such devices often fails. It is therefore an object of the present invention to provide a wireless modem which provides greater communication integrity.

Contents of the invention

In accordance with the present invention, a wireless modem system is provided which protects the integrity of communications by providing automatic RF signal detection to lock on to a selected channel following a handshaking process. In particular, the modem functionality for modulating and demodulating data to and from a computer for transmission over an analog telephone line exists only in remote wireless modems.

According to the present invention there is provided a wireless modem system comprising: a first and a second device, the first device comprising: means for being coupled to a computer for receiving data from the computer; means for encoding data and transmitting received data using a digital radio transmission format; and the second device includes means for receiving data transmitted from the first device in a digital radio transmission format and further processing it into an analog format for Apparatus for transmitting over a wired telephone network, wherein each of said first device and said second device is adapted to transmit and receive data over a plurality of radio frequency channels, the data being added to the channels in a spread spectrum sequence and wherein the first device and the second device include automatic channel detection means, after a handshake process between the first device and the second device, the automatic channel detection device locks on the the most available channel among the plurality of radio frequency channels to maintain the integrity of communications therebetween.

According to the present invention, there is provided a wireless modem system comprising: first and second devices, each of which has: a port for receiving serial data; Signal conversion means for converting serial data into parallel data coupled to said port; storage device having a transmitter buffer and a receiver buffer; control means for generating data packets from data originating from said signal conversion means ; means for coupling said data packet to said transmitter buffer; a transceiver for receiving and transmitting data via a plurality of channels; for adding data in said transmitter buffer to a repeating sequence means for a selected channel of said plurality of channels; and means for storing data packets received by said transceiver into said receiver buffer, said control means being adapted to buffer said receiver The packets in the zone are transmitted to the signal conversion means, wherein the first device and the second device are capable of transmitting and receiving data simultaneously; and the first device and the second device include automatic channel detection means, the automatic channel The detecting means locks on the selected channel among the plurality of channels after a handshake process between the first device and the second device to maintain the integrity of communication therebetween.

Description of drawings

Figure 1 shows a block diagram of an exemplary embodiment of a wireless modem system in accordance with the present invention.

FIG. 2 shows a flowchart for power-on initialization of the device shown in FIG. 1 .

The flowchart in FIG. 3 is used to represent a continuous operating loop RL which performs alignment bit monitoring and receive data buffer monitoring for reception in the device shown in FIG. 1 .

FIG. 4 shows a flowchart for data transmission by the device shown in FIG. 1 .

FIG. 5 shows a flowchart for UART/modem interrupt processing by the device shown in FIG. 1. FIG.

FIG. 6 shows a flow chart of data reception by the device shown in FIG. 1 .

FIG. 7 shows a flowchart for a channel tracking timer interrupt for packetless reception by the apparatus shown in FIG. 1 .

FIG. 8 shows a schematic diagram of a main processor used in the device shown in FIG. 1 and includes an SST (Spread Spectrum Technology) processor and an SRAM used in the device shown in FIG. 1 .

FIG. 9 shows a schematic diagram of a UART, LED indicator and RS-232 interface for the device shown in FIG. 1 .

FIG. 10 shows a schematic diagram of an RF transceiver for use in the device shown in FIG. 1 .

FIG. 11 shows a schematic diagram of a power supply for the device shown in FIG. 1 .

12 and 13 show circuit diagrams of the apparatus shown in FIG. 1 .

Detailed ways

The wireless modem (WM) device described herein for use in a wireless modem system and also referred to as a wireless modem jack (WMJ) or RF link operates in the ISM band (902-928 MHz), for example 900 Mz. The wireless modem system includes, for example, a base unit 1000 and a wireless remote modem unit 10001 as shown in FIG. Both units are capable of sending and receiving data/fax simultaneously. The only difference is that the base unit 1000 does not require a "modem" function (e.g. 18') and associated telephony processing (e.g. 20'), since data is modulated and demodulated into Analog signals sent and received in 1001.

The design of the system is preferably based on Direct Sequence Spread Spectrum (DSSS) technology, which also provides maximum security for data transmitted in the radio spectrum, especially in the 900MHz range. Currently, the maximum data transfer for WMJ can reach 115Kbps (via radio frequency link), which is a much higher speed when compared to a conventional hardwired modem connection. WMJ can be used for Internet business connections, as well as for sending/receiving fax data and for transferring other types of data. All transmissions are in the form of SST digital encryption.

Thus, the present invention allows the RF link to support data rates up to 115 kbps with error detection and correction. It is compatible with the V.90/56K high-speed paging technology (flex) modem standard

capacity, allowing it to be used with many existing Internet service providers. As described below, the system provides automatic RF signal detection and locking to the channel selected for both units (following an identified handshake procedure).

Since the base unit 1000 includes a serial port, the system can be used not only as a conventional modem for accessing a computer network via a telephone line, but also for remote printer sharing, a network connection between two PC terminals. The system can also support hyper terminal data transmission.

Furthermore, since the modulated signal is in digital form, the FCC allows a maximum transmission power equal to (1) watt instead of 100 milliwatts in the analog modulation type. This will allow for better range of transmission, typically up to a range of 300 feet (or better) in residential environmental conditions.

Today, personal computers (PCs) and the Internet are becoming more and more popular all over the world. Most consumers can access the Internet using an ordinary connection through a regular telephone jack. Unfortunately, most residential homes only have one or two telephone wall jacks throughout the house. Therefore, installing a PC in a location far from a telephone wall jack is problematic for most people.

Using WMJ, a consumer can, for example, access the Internet or send/receive faxes, or transfer files between two PCs anywhere across the room. The data (signal) may be in digital form encrypted by the signal. Radio frequency (RF) signals may be in the range of 900MHz; from 902-928MHz. WMJ design is based on digital spread spectrum technology. Thus, WMJ is capable of sending and receiving signals over greater distances (approximately 300 feet) than any 900MHz device that sends a signal in a conventional analog modulation format. Part 15 of the FCC rules allows 1 watt of RF output power for any device with a digital modulation format, compared to a device with an analog modulation format that is only allowed 100 milliwatts of output power.

Discussion Figure 1 is a block diagram for the base unit RF chain. The overall operation is described first for the case where the RF link transmits data from a PC not shown, and then for the case where the RF link receives data from an RF link transmitter not shown. It should be noted here again that the only difference between the base unit 1000 and a remote unit or extension 1001 is that the remote unit additionally has an embedded modem function 18' and additional circuitry for interfacing an RJ-11 jack to the telephone network 20'. Therefore, to avoid redundancy, the following description mainly focuses on the basic units.

The DCE port 2 is coupled to a PC computer, not shown, and transmits the received serial digital data to an interface 4 which adjusts the voltage level of each bit to a standard value. UART 6 converts the serial data to parallel data, and processor 14 constructs a data packet with an alignment bit, a leading byte, message byte and trailer byte. Then, the packet is stored in a Tx buffer in SRAM8. The SST 10 looks for an unused channel in the RF module 12, reads data from the Tx buffer in the SRAM 8, and supplies the data to the channel of the RF module 12 in a repeating sequence. All actions are controlled by MCU 14 and LED indicators 16 indicate various operating situations.

When the RF link of FIG. 1 is to receive data from an external RF link, the SST scans the channels of the module 12, and the data received therefrom is transferred by the SST to an Rx buffer not shown in SRAM8. Under the control of the MCU 14, the data in the data packet is restructured and transferred to the UART 6, where the parallel data is converted into a serial bit stream, which is transferred to the interface 4 before being applied to the DCE port 2 coupled to another PC. to adjust the voltage.

initialization

Discussion is now made of the flow chart in FIG. 2 which illustrates what happens when power is turned on, as shown at 22, either in a base unit or in an expansion unit. If the test in the cell's SRAM 8 indicates that no more is defective due to not operating the SRAM 8 correctly, then no operation is performed. At decision diamond (hereinafter "decision block") 26 it is determined whether something is coupled to DCE port 2 . If something is coupled, eg a PC, and if it is a base unit BU, as shown in Figure 1, then the modem 18 is ignored and the BU must be set as master-slave as shown at 28. The main bit of DIPSW1 as shown in Figure 8 is tested. If the switch is on (or set in the 'up' position), a corresponding master bit of the OPSTAT (operational status) register is set. Otherwise, the bit is cleared. Usually an extension unit (EU) is always set as a master unit (the unit that initiates the transmission) and a base unit (BU) is set as the slave unit (the unit that is always in listening mode). For applications that do not require modem functionality, two BUs can be used. In this case, one BU must be set as 'Master' and the other as 'Slave'. If desired, a BU (serial port selected) can also be set as master, while another BU (serial port selected) or an extension unit EU is set as slave.

If, as indicated by decision block 30, a master setup is made, then as indicated by 32, the channels of the RF module 12 are scanned. The master unit monitors the RSSI (Received Signal Strength Indicator) of the individual RF channels for 100 milliseconds. All ten RF channels (0-9) are scanned. Then, choose a channel that is the quietest. Afterwards, the master unit monitors the channel for any transmission activity. If not, that channel is selected for transmission. A timer of the MCU 14 is used for the channel scan timer handled by a chscan_to interrupt service routine.

After the channel is selected, as indicated at 34, a no packet received timer is started. This forces itself into the link establishment process when the timer expires. Then, follow the process of Figure 7. Then, at 36, the appropriate registers for the Rx buffer and HDx (transmit or receive mode of operation) are set. At this point, the unit enters the run-time 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 set the baud rate of UART6 at 38 and start the tracking timer at 40. This function is only performed in a slave unit and consists of scanning the RF channel of a master unit. As an example, each channel is scanned for 20 milliseconds.

With reference to decision block 26, if DTR is not activated, then at 42 it is checked to see if modem 18 is installed. If yes, the unit is set as slave and the modem Rx is interrupted at 44 , meaning no communication with the modem takes place, and continues to block 36 . If not, the slave enable UART Rx interrupt is set at 46 and the routine returns to block 28.

run time loop

After completion of the setup routine in FIG. 2 , the radio link enters a runtime loop of continuous operation as shown in FIG. 3 . At decision block 48, a query is made to see if 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 already been received. If it has been received, go to RBUF in a service routine where the data is stored in the Tx buffer in SRAM8 or in the Rx buffer. This small cycle is repeated until no alignment byte is received. If there is no indication of the alignment byte at 48, then at 50 a check is made to see if an RF link has been declared up, meaning that a handshake has been completed so that the RF link is ready to send data. If not, there is no use in progress, and the process returns to the beginning of the loop. However, if at 50 an RF link connection has been declared, then at 52 it is determined whether there is any data in the Rx data buffer of SRAM 8. If so, it is sent either to UART 6 or to modem 18, as indicated at 54, depending on which type of operation occurs. The unit forwards data from the receiver buffer to UART6 for the base unit BU only if the DTR is active (eg PC connected to the port is not ready) and the link is in 'up' state. Modem functionality is only relevant to BU. Writing to/reading from UART6 or the modem corresponds to writing to/reading from the FIFO buffer of the UART6 or the modem. After the data is sent, the process returns to the beginning of the loop.

transmission

As shown in FIG. 4, data transfer is performed starting at 56. First, any data in the TX buffer in SRAM8 is transferred. First, it is checked at 58 whether a retransmission bit has been received as a request for a retransmission as shown in FIG. 7 . If yes, at 60 the pointer in the TX buffer in SRAM 8 is restored, but if not, at 62 the data is read from the Tx data buffer. At 64 the Tx buffer pointer is saved and as shown at 66 a data packet is constructed in UART6. Data is copied from the send buffer of SRAM8 to the data part of the packet buffer (register of MCU). The number of bytes in one data packet is 0 (zero) to 72. A packet envelope is added. The envelope includes packet header bytes, link control bytes, packet length (number of header bytes to last byte of checksum), and channel number/unit identification bytes.

At 68, the routine calculates and adds a 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 trailer bytes (0xff) are added to the end of the packet transmission.

At 70, it is checked whether the RF link is set to a master unit by a manual switch. If yes, then at 72 a No Packet Received timer is started and the process as shown in Figure 7 and to be described then follows.

The flowchart in Figure 5 represents the steps for the UART/Modem Interrupt Handling Service 102, where at 104 data is read from the UART6 or Modem Rx FIFO. At 106, until the buffer is empty, then written to the Tx data buffer, and at 108, return to start of transmission 56 of FIG. 4 .

take over

Discussing FIG. 6, beginning at 74, the routine monitors for two consecutive alignment bytes (0x80). These bytes may not be properly aligned. The unit reads and aligns the seven bytes of data (6 to 78) in the packet. If the packet length exceeds 6 (but not greater than 78), the unit reads the remaining bytes from the SST and stores them in the packet buffer (register of the MCU). If a header byte is received according to decision block 76, then as shown at 78, data is read from the SST Rx FIFO in SRAM 8. At decision block 80, the validity of the data packet is checked. At decision block 82, it is checked whether the address of the data is the address of the receiving RF link. This is a program function in MCV8 of both units to check if link up or link down for a packet is set in order to prepare master and slave units for transmission. This prevents getting an adjacent transfer. At block 84, the RF link is declared connected based on a light indicating that the link is ready to receive, and at 86 it is checked whether the master/slave switch is set in the slave position. If so, then at 88 the user can set the baud rate with a combination of switches or through software. Usually, the baud rate is set to the maximum value. See Fig. 7, at 90 a no packet received timer is started, and at 92 a link setup packet is established in the MCU 14 to request more data from the buffer. If decision block 86 indicates that it is a master unit, then at block 87 data is sent and the run time loop of FIG. 3 is entered.

Discussing again decision block 82, when a link setup packet indicates that it is not being received, at 94, if the data packet is received in sequence, it is written into the Rx data buffer of SRAM 8 and sent 100. A NO indication from any of decision blocks 76 , 80 , and 94 returns the process to the run-time loop of FIG. 3 .

Figure 7 shows the No Packet Received/Channel Tracking Timer interrupt processing routine for the master and slave. If, as determined by decision block 110, two data links are established, ie if a handshake has been performed between them, then at 112 a timeout counter is read. If there is a transmission interruption, the timeout counter starts counting. A timeout counter starts running as each data packet is transmitted, and the clock is set back to 0 when the last or tail byte of a message passes. Therefore, if at decision block 114 the counter is not zero, it means that the data packet was not completely sent, in which case a retransmission bit is sent back to the sender. This is the retransmission bit referred to in decision block 58 in FIG. 4 illustrating transmission. After this, the process returns to decision block 110 .

A timeout counter is maintained and used by the master and slave units to declare link down. The value of the counter is different for master and slave unit, ie 10 and 1 for master and slave unit respectively. Furthermore, the value of the NPR (No Packet Received) timer is different for both master and slave units, ie 500 milliseconds and 1000 milliseconds for master and slave units respectively.

For the master unit, if no valid data packet is received from the slave unit within 50 milliseconds after sending a data packet, the master unit resends the data packet. Ten consecutive expirations of the NPR timer declares the link down and the master unit re-enters the channel scanning process. The counter is reloaded each time a valid data packet is received. The value of NPR should be sufficient for the longest data packets. Data packets vary in length from 6 to 78 bytes, excluding preamble, alignment and trailer bits.

Since the slave unit is always in listening mode, ie never initiates data packet transmission, only one NPR expiration is sufficient to indicate that the link is closed. The value of NPR is chosen to cover the total time the master unit tries to receive a response from this slave unit by resending a data packet, ie 10 x 50 milliseconds. After declaring link down, the slave unit "plays dead" for another 1000 milliseconds to ensure the master unit declares link down and restarts link establishment. Note that the aforementioned mechanism is not used during link establishment, since the master will keep sending link establishment as long as no response is received from the slave.

However, if at decision block 114 it is indicated that the timeout counter has returned to 0, then both the master and slave units have finished transmitting, but they will remain in handshake mode until it is determined at decision block 116 whether it is a master or a slave . If the master device, then at 117 the SST 10 scans the channels as shown in blocks 32 and 34 of FIG. 2 .

On the other hand, if decision block 116 indicates that the RF link is not the master unit, and is therefore a slave unit, then at block 126 the master unit is told to declare the link closed, i.e. to declare the end of transmission for both master and slave units, but they maintain in handshake mode. At 128, available channels are found. At block 124, these are used in DSS mode, where a tracking timer is started to sequentially send data in the available channels.

If the indication at decision block 110 is that the link between the RF units has not been properly established, ie the link is not connected. If at decision block 120 it is determined that it is not the master unit, ie it is a slave unit, then block 122 finds an available channel in the same way as block 124 . If the indication at decision block 120 is that it is the master unit, then at block 126 a data packet is sent and at block 128 a no packet received timer is started.

In discussing the schematic diagrams of FIGS. 8-13, it should be understood that the specific microchips specified are merely examples that may be used. They may be designated by their "U" numbers and their acronyms.

FIG. 8 is a schematic diagram in which MCU 140 is the main processor of _U4 . The pattern U ₆ for testing the SRAM 8 as in block 24 of FIG. 2 and the answer U ₆ of the SRAM are carried by the data path 130 . Switches for providing RF link identification, baud rate and whether a unit is master or slave are indicated at 132 and are coupled to pins 138 of MCU U ₄ through buffer 134 and data paths. Oscillator 138 provides SST chip 141 with RF to GFSK transceiver 142 of FIG. 10 via wire 144 and it provides an RF channel to antenna 145 of FIG. 10 . No attempt has been made to describe every connection, since each connection is believed to be known to those skilled in the art from what has been shown and described how to practice the invention.

The schematic diagram in FIG. 9 shows the UART as U ₁₀ and the RS-232 interface process 4 at 146 . The DCE communication port 2 is indicated at 148 and at 150 LEDs for indicating various operating conditions.

The schematic diagram in FIG. 11 shows a power supply 152 for a base unit such as that shown in FIG. 1 and a power supply 154 for an expansion unit.

The schematic diagrams in Figures 12 and 13 show the modem 18 which allows the extension unit to communicate with the Internet. It includes _U18 and _U18 and has a plug 154 for coupling to a telephone line.

Numerous modifications, as well as alternative embodiments, of the invention will be apparent to those skilled in the art from consideration of the foregoing description. Therefore, the description is for illustration only and is intended to teach those skilled in the art the best mode of carrying out the invention. Modifications may be made to the details of the examples without departing from the spirit of the invention, and the sole use of all modifications within the scope of the appended claims is reserved.

Claims (7)

1. wireless modem system comprises:

First and second equipment,

First equipment comprises:

Be used to be coupled to a computer so that from the device of this computer receiving data;

Be used for digital coding that is received and the device that uses a kind of digital radio transmission form that the data that received are sent; And

Second equipment comprises:

Be used to receive send the data that form sends and further it is treated as analog format with digital radio and be used at the online device that sends of telephone from first equipment, in wherein said first equipment and described second equipment each all is suitable for being transmitted and receive data by a plurality of radio-frequency channels, and these data are added in the channel in spread-spectrum sequence mode; And

Wherein said first equipment and second equipment comprise the automatic channel checkout gear, after the handshake procedure of this automatic channel checkout gear between described first equipment and second equipment, be locked in according to the standard of predesignating and keep the integrality of communicating by letter on the available channel in described a plurality of radio-frequency channel therebetween.

2. the system of claim 1 is wherein used digital radio transmission form and is sent to second equipment from the data that described computer receives by described first equipment at the most available channel.

3. the system of claim 1, wherein second equipment comprises a modulator-demodulator that is used for further the transmission data processing that is received being become analog format.

4. the system of claim 3, wherein modulator-demodulator receive and demodulation from the analog signal of cable telephone network.

5. wireless modem system comprises:

First and second equipment, each in the described equipment has:

A port that is used to receive serial data;

The serial data that is used for being added to its any side is converted into the chromacoder of the parallel data that is coupled to described port;

Memory device with a transmitter buffering area and a receiver buffering area;

Generate the control device of packet from the data that are derived from described chromacoder;

Be used for described packet is coupled to the device of described transmitter buffering area;

A transceiver that receives and send data through a plurality of channels;

Be used for the data of described transmitter buffering area are added to repetitive sequence the device of selecteed channel in described a plurality of channel; And

Be used for the packet that described transceiver receives is stored into the device of described receiver buffering area, described control device is suitable for the grouping in the described receiver buffering area is sent to described chromacoder, and wherein said first equipment and described second equipment can transmit and receive data simultaneously; And described first equipment and second equipment comprise the automatic channel checkout gear, are locked in after the handshake procedure of this automatic channel checkout gear between described first equipment and described second equipment to keep the integrality of communicating by letter in described a plurality of channel on the selecteed channel therebetween.

6. according to the system of claim 5, comprise also being used to scan the device of described a plurality of channel that described channel is used as described selecteed channel with the identification clear channel.

7. according to the system of claim 5, also comprise:

In each of described first and second equipment, be used for selectively determining the hand-guided device of its address;

In each of described first and second equipment, be used for determining the hand-guided device of the address of other radio-frequency apparatus;

In described first and second equipment, be used for the address of its address and other equipment is write the device of its transmitter buffering area;

In described first and second equipment, be used for reception, the known address of other radio-frequency apparatus of device will compare with to(for) institute's receiver address of other equipment in response to itself address; And

If it is identical then carry out further communicating devices to be used for the address of being compared.

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