Multiplex communications – Communication over free space
Reexamination Certificate
1997-10-20
2002-04-16
Patel, Ajit (Department: 2662)
Multiplex communications
Communication over free space
C370S465000
Reexamination Certificate
active
06373827
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to telecommunication systems. More particularly, this invention relates to full-duplex transmission and reception of voice, data, and image signals over multiple communication media.
2. Background of the Related Technology
T-carrier systems have become an essential part of modern telecommunications systems. A T-carrier system is found in every telephone company in North America. A T-carrier allows for transmission of one or more telephone calls or data connections by modem. The basic unit of signaling is DS0, followed by progressively higher speed signaling rates. First generation T-carrier systems, called T1, which carry Digital Signal Level 1 (DS1), employ a full duplex all-digital service. The digital stream is capable of carrying standard 64 kilobits per second (kbps) channels in which 24 channels are multiplexed to create an aggregate of 1.536 Mega bits per second (Mbps). Time division multiplexing (TDM) allows a channel to use one of 24 timeslots. More particularly, the 24 channels are time-division multiplexed into a frame to be carried along the data stream line. Typically, each frame contains one sample of 8 bits from each of the channels, and a framing bit. This structure results in a frame having 193 bits. In view of employing pulse code modulation (PCM) on each channel, there are 8000 frames per second. Hence, a frame is 125 microseconds long. Eight kbps of overhead bits are added (due to framing) to 1.536 Mbps, thereby yielding an aggregate of 1.544 Mbps.
A T1 system employs Alternate Mark Inversion (AMI) coding to reduce the required bandwidth of 1.5 MHz by a factor of two. The transmission is byte-synchronous whereby timing synchronization for each channel is derived from the pulses that appear within the samples (8 bits in each sample). This timing keeps everything in sequence. Although, a T1 system employs generically 24 channels of 64 kbps data plus 8 kbps of overhead (sometimes referred to as channelized service), the multiplexing equipment may be configured in other ways. For example, T1 may be used for a single channel of 1.536 Mbps, two high-speed data channels at 384 kbps each, and a video channel at 768 kbps. In short, a T1 system service does not have to be channelized into 24 timeslots. It can be split into any number of usable data streams.
T1-systems may multiplex T1 signals into a T2 (DS2) system, but with additional framing bits and 4 times the data rate. This results in an aggregate data rate of 6.312 Mbps. Similarly, a T3 digital link comprises a multiplexing of 7 T2 links (and additional framing bits), resulting in a data rate of 44.736 Mbps. The T3 system has greater demand in high capacity applications.
The E carrier services are the European equivalents of the T-carrier. The following table contrasts the various T and E carrier systems in terms of their TDMA structure and data rates.
Carrier
TDMA Structure
Data rate
DS0
8 bits/125 &mgr;sec
64
kbps
T1, DS1
24 DS0 + 1 Framing bit = (24 × 8 + 1)
1.544
Mbps
bits/125 &mgr;sec
T2, DS2
4 DS1 + 17 Framing bits =
6.312
Mbps
(4 × 193 + 17) bits/125 &mgr;sec
T3, DS3
7 DS2 + 69 Framing bits =
44.736
Mbps
(7 × 789 + 69) bits/125 &mgr;sec
E0
N/A
64
kbps
E1
30 E0 + Framing Bits
2.048
Mbps
E2
4 E1 + Framing Bits
8.448
Mbps
E3
4 E2 + Framing bits
34.368
Mbps
Due to the considerable cost associated with wiring and line amplifiers, there has been an increasing need for wireless implementation of T/E-carrier technology. To meet this need, initially infrared laser-based T1/T2 systems were developed. Since no licensing is required, the system may be placed in service as soon as it is installed. In addition, the implementation cost requires no major towers, power equipments, cable entrances or other similar construction equipment. Typical applications of such cordless T1/T2 links are digital PBX to PBX connection (using a quad T1), video conferencing using a channel capacity of 6 Mbps, or four 1.544 Mbps systems having a compressed video standard. However, the infrared laser technology has a number of disadvantages, such as limited range (up to 1.5 miles), concern over the use of a laser in an office environment, atmospheric disturbances, etc.
One limitation of conventional T/E carrier systems for synchronization between the transmitter and the receiver is that they use framing overhead bits on successive frames. More particularly, frames are sent sequentially to ensure synchronization. Furthermore, initial T/E systems are used to reduce the number of voice frequency cable pairs needed for interconnecting telephone offices. Many of these cable pairs do not support long links, and are not cost efficient. More importantly, there are technical complications associated with the T/E systems as they became more widely deployed. One major complication is that the speech coding is inadequate for providing proper transmission quality to create long-distance circuits. To prevent this problem, the number of T systems in series has to be limited to three, which substantially complicates network provisioning and circuit planning.
In view of the foregoing, there is a need in the industry for a new system and method of implementing T/E systems which extends the coverage area in a wireless communication environment without the disadvantages of conventional methods. The new system and method should enable compensation for transmitting and receiving frequency variations, synchronization at the receiver and provision of a virtual signaling channel. These systems should expand coverage areas while maintaining minimal channel inter-cell interference or congestion. Furthermore, such system should be easy to install and maintain. Moreover, the system should support communication for mountainous region extension, urban links between separate facilities, over water extension, site interconnections of cellular networks, building-to-building LAN extensions, PBX, FAX and data extensions, and community networks.
SUMMARY OF THE INVENTION
To overcome the problems associated with the related technology, the invention provides a system and method of communicating voice, data, and image signals over multimedia signal paths transparently. A wireless transceiver station (WTS) is provided to communicate signals from inputs having various standardized signaling schemes to outputs having a single signaling scheme. The various standardized inputs include signals conforming to the DS0, T1/E1, T2/E2, and T3/E3 signaling standards (“signaling schemes”). The outputs of the WTS system generate signals for transmission over one of a variety of selectable transmission media such as the ISM, NII, and PCS bands, for reception by another WTS system at a distant site. At the distant WTS site, the received signals are amplified and processed back to their original, or other selectable, standardized signaling scheme. The processed signals are then forwarded to their intended destinations. Using the WTS system, the intelligence and signaling scheme of the signals are preserved.
According to one embodiment of the invention, a wireless multimedia carrier (WMC) system comprises two or more WTS systems. Each WTS comprises three main subsystems. These subsystems include a radio frequency (RF) system, an intermediate frequency (IF) system, and a baseband/digital signal processing (Baseband) system. One WTS is designated as a local WTS receiving signals having a standardized telephonic signaling scheme (e.g., T3/E3) from a local communication facility. The local WTS converts the standardized telephonic signaling scheme to a RF signaling scheme, and transmits RF signals having the RF signaling scheme to another WTS. The RF signaling scheme includes applying a signal access method such as TDMA and/or CDMA. Another WTS is designated as a distant WTS receiving the RF signals from the local WTS. The distant WTS converts the RF signaling scheme to the standardized telephonic signaling scheme.
REFERENCES:
paten
Bui Hoang Xuan
Hatim Baya
Karacaoglu Ulun
Lakkis Ismail
Nche Chi
Patel Ajit
Wireless Facilities, Inc.
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