Multiplex communications – Communication over free space – Repeater
Reexamination Certificate
1998-12-31
2004-03-30
Ton, Dang (Department: 2666)
Multiplex communications
Communication over free space
Repeater
C370S347000, C455S013400
Reexamination Certificate
active
06714522
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wireless local loop system, and more particularly, to an improved data transmission/reception apparatus for a WLL system using a CDMA method.
2. Description of the Background Art
In general, a wireless local loop (hereinafter, “WLL”) system employs a wireless communication network instead of wired network, between subscribers' terminals and a telephone company and enables data communication, i.e., internet, as well as voice communication using traffic channels.
FIG. 1
is a schematic block diagram illustrating a general WLL system. As shown therein, the system includes voice purpose or data purpose terminals
10
, a subscriber' radio interface unit
20
interfaced to the terminals
10
, a base station
30
for wireless data reception/transmission with the subscriber's radio interface unit
20
, a base station controller
40
for controlling the base station
30
, and a WLL switching center
50
for forming a wired communication pathway to enable a voice or data communication for example through internet via PSTN (Public Switched Telephone Network) or PSPDN (Public Switched Packet Data Network).
More specifically, the subscriber's radio interface unit
20
performs a wireless interface between the base station
30
and the subscriber's terminal
10
and it is connected to a telephone set, facsimile machine or computer through an analog or digital data path so as to enable voice and data service.
The base station
30
is interfaced to the base station controller
40
and it is interfaced through wireless channel to the subscriber's radio interface unit
20
so as to form a data path from the base station controller
40
to the subscriber's radio interface unit
20
.
The base station controller
40
performs major roles of the WLL system such as a call processing for a reception/transmission signal, base station management and voice signal compression. The WLL switching center
50
serves to interface telephone network or data network (PSTN/PSPDN) with wireless subscribers' network.
FIGS. 2 and 3
specifically illustrate the subscriber's radio interface unit
20
and the base station
30
, wherein the two apparatuses
20
,
30
carry out similar performance with similar construction.
First, as shown in
FIG. 2
, the subscriber's radio interface unit
20
includes a duplexer
21
for switching transmission/reception signals, an RF receiver
22
for down-converting the signal from the duplexer
21
, a demodulator
23
for demodulating the down-converted signal, a decoder
24
for decoding the demodulated signal, a vocoder
29
connected to a voice class terminal and for encoding a voice signal, a DPU (Data Port Unit)
28
serving as a terminal connection apparatus for data, an encoder
27
for performing a convolutional coding with regard to a voice signal or data signal from the DPU
28
or the vocoder
29
, a modulator
26
for modulating the encoded signal, and an RF transmitter
25
for up-converting the modulating signal.
The RF receiver
22
includes a BPF (Band Pass Filter)
22
-
1
for filtering a signal received through the duplexer
21
, a LNA (Low Noise Amplifier)
22
-
2
for amplifying the filtered signal into low noise, and a down converter
22
-
3
for down-converting the amplified signal into a low pass band signal.
Also, the RF transmitter
25
includes an up converter
25
-
1
for up-converting the signal from the modulator
26
into a high frequency signal, a PA (Power Amplifier)
25
-
2
for amplifying the frequency-converted signal to a predetermined level, and a BPF
25
-
3
for filtering the amplified signal.
As further shown in
FIG. 3
, the base station
30
is similar in construction and operation to the subscriber's radio interface unit
20
in FIG.
2
and its description will be omitted, accordingly.
With reference to
FIGS. 1 through 3
, the conventional voice or data transmission/reception steps for a WLL system will now be described.
Initially, according to the data transmission steps from a subscriber's side, the voice signal from a voice class terminal such as a telephone set is converted to a PCM (Pulse Code Modulation) signal through a vocoder
29
and applied to the encoder
27
through the PCM bus. The data signal from the data-purposed terminal such as a PC (personal computer) is applied to the encoder
27
through the DPU
28
.
Then, the encoder
27
converts the applied PCM signal to a convolutional code, and the converted signal is modulated by the modulator
26
and applied to the RF transmitter
25
. The applied signal is converted to a high frequency signal by the up converter
25
-
1
and amplified to a predetermined power level demanded through the PA
25
-
2
and it is also filtered through the BPF
25
-
2
and transmitted into a free space.
The base station receives the data from the subscriber' side according to the aforementioned steps and its wireless communication steps will now be explained.
The signal received via the antenna through the free space is applied through the duplexer
31
to the RF receiver
32
, and the RF receiver
32
filters the signal received through the duplexer
31
and amplifies the filtered signal to the LNA, thereby down-converting the amplified signal to a low pass band signal.
The down-converted signal is demodulated by the demodulator
33
and decoded by the decoder
34
. Then, the voice signal passes through the PSTN and the data signal passes through the PSPDN, thereby enabling the subscriber to perform data communication with another subscriber or internet network. Those steps are similarly carried out when transmitting data from a base station to a subscriber.
The conventional WLL system employs a circuit switching method to implement the transmission/reception of voice or data. According to the circuit switching method, when an exchanger starts interfacing from a signal-transmitting terminal, a channel to a signal-receiving terminal is determined and the channel is seized until the communication is terminated, thereby transmitting/receiving communication information. For example, a telephone network follows the circuit switching method.
FIG. 4
is a flow chart schematically illustrating data transmitting/receiving steps in the conventional WLL system. As shown therein, the base station determines whether a hook off/on signal is output from a subscriber's terminal for notifying a communication start/end in step Si. When the hook off signal notifying a communication start is transmitted, it is identified whether there is an unoccupied channel in step S
2
. When all the channels are in use, a busy tone is generated and transmitted to the terminal in step S
3
and when there are unoccupied channels, one of the unoccupied channels is assigned in step S
4
.
Then, in step S
5
the terminal serves to transmit voice or data through the assigned channel, wherein the assigned channel remains seized until the voice or data communication is terminated, that is, until the hook on signal is sensed.
The thusly operating conventional WLL system permits simultaneously communicable multiple channels to be assigned to a single base station. The respective base stations form wireless communication channels between subscribers using down-converting and up-converting different frequencies through a plurality of limited channels.
The subscribers-housing capacity per base station in the conventional WLL system is presumed to range 10 times as large as the wireless channel number. Here, the subscribers include telephone subscribers using voice communication, fix subscribers, and data communication subscribers interfaced to personal computers and work stations for internet or data communication.
The reason why the subscribers capacity is assumed to be ten times as large as the channel number is that voice communication subscribers generally terminate the communication within 3 minutes according to local statistics in South Korea.
In the WLL system performing a data
Fleshner & Kim LLP
LG Information & Communications Ltd.
Ton Dang
Tran Phuc
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