Telecommunications – Receiver or analog modulated signal frequency converter – Frequency modifying or conversion
Reexamination Certificate
1998-11-17
2001-06-12
Nguyen, Lee (Department: 2683)
Telecommunications
Receiver or analog modulated signal frequency converter
Frequency modifying or conversion
C455S039000, C455S134000, C455S161200, C455S161300, C455S226100, C455S226200, C455S311000
Reexamination Certificate
active
06246867
ABSTRACT:
BACKGROUND
The present invention relates to homodyne radio receivers, and more particularly, to a method and device which reduces the amount of current required to perform signal strength measurements within homodyne receivers.
Communication systems that communicate voice and data messages are extensively used in telephony and wireless communication systems. For example, European Telecommunication Standard Institute (ETSI) has specified a Global Standard for Mobile Communication (GSM) that uses time division multiple access (TDMA) to communicate control, voice and data information over radio frequency (RF) channels. In the U.S., Telecommunication Industry Association (TIA) has published a number of Interim Standards, such as IS-54 and IS-136, that define various versions of digital advanced mobile phone service (D-AMPS), with the capability of transmitting voice and data to subscribers. These types of communication system covers a geographical area that is subdivided into communication cells, which together provide communication coverage to a service area, for example, an entire city.
In a GSM communication system, for example, each cell is served by one or more base stations that communicate with mobile stations over down link and uplink RF channels. The RF channels are subdivided into a number of time slots, which are known as logical channels. Speech or data is transmitted during logical channels designated as traffic channels (TCH) and signaling information pertaining to call management in the system, including, synchronization and hand over are handled over control channels. In the GSM system, control channels are grouped as broadcast channels (BCH), common control channels (CCH), dedicated control channels (DCCH), and SMS broadcast channel (S-BCCH). BCHs are used for frequency correction, synchronization, and communicating cell specific information. BCHs, which are mapped on time slot
0
of an RF channel, include frequency correction channel (FCCH), synchronization channel (SCH), and broadcast control channel (BCCH). FCCH is used for transmitting a sine wave signal, which serves to identify the BCH and to enable the mobile stations to synchronize to the BCH frequency. The SCH is used to synchronize the mobile stations with the TDMA frame structure within a particular cell and to identify a chosen cell as a GSM cell using a Base Station Identity Code (BSIC), which identifies the cells in the handover process.
CCHs, which are mapped over a number of time slots, are used for access and allocation of signaling control channels. CCHs include paging channel (PCH), access grant channel (AGCH), and random access channel (RACH). PCH is a paging channel used for alerting a called mobile station using a mobile station identity number (IMSI). AGCH is used for assigning a signalling channel. RACH is used by the mobile stations for requesting a call initiation or answering with a channel request when called. Conventionally, the base stations transmit messages to the mobile stations over one or more allocated downlink control channels with full power if there is no traffic in the cell, in order to enable the mobile stations to synchronize for communication within a cell.
Preferably, the communication cells are patterned according to a cell pattern that allows some of the spaced apart cells to use the same uplink and downlink RF channels. In this way, the cell pattern of the system reduces the number of RF channels needed to cover the service area. The RF channels are planned in a way that reduces interference to improve system performance in terms of call set-up and handover. A sparse reuse is required for the BCCH frequencies which today often are planned in a 12 reuse pattern. It is, however, desirable to plan the RF channels in a tighter reuse pattern, which is of particular importance when communicating within a limited spectrum of for example 5-6 MHz. Because the control channel resources are a large portion of the total available spectrum, tighter control channel reuse increases traffic capacity by allowing more RF channels to be allocated as TCHs. A tighter channel reuse, however, results in performance degradation of the control channels.
In an IS-54 standard system, each TDMA frame consists of six consecutive time slots and has a duration of 40 milliseconds (msec). Thus, each radio channel can carry from three to six DTCs (e.g., three to six telephone conversations), depending on the source rates of the speech coder/decoders (codecs) used to digitally encode the conversations. Such speech codecs can operate at either full-rate or half-rate. A full-rate DTC requires twice as many time slots in a given time period as a half-rate DTC, and in the IS-54 standard, each full-rate DTC uses two slots of each TDMA frame, i.e., the first and fourth, second and fifth, or third and sixth of a TDMA frame's six slots. Each half-rate DTC uses one time slot of each TDMA frame. During each DTC time slot, 324 bits are transmitted, of which the major portion, 260 bits, is due to the speech output of the codec, including bits due to error correction coding of the speech output. The remaining bits are used for guard times and overhead signaling for purposes such as synchronization.
It can be seen that a TDMA cellular system operates in a buffer-and-burst, or discontinuous-transmission, mode: each mobile station transmits (and receives) only during its assigned time slots. At full rate, for example, a mobile station might transmit during slot
1
, receive during slot
2
, idle during slot
3
, transmit during slot
4
, receive during slot
5
, and idle during slot
6
, and then repeat the cycle during succeeding TDMA frames. Therefore, the mobile station, which may be battery-powered, can be switched off, or sleep, to save power during the time slots when it is neither transmitting nor receiving.
In addition to voice or traffic channels, cellular radio communication systems also provide paging/access, or control channels for carrying call-setup messages between base stations and mobile stations. According to the IS-54 standard, for example, there are twenty-one dedicated analog control channels (ACCs), which have predetermined fixed frequencies for transmission and reception located near 800 MHz. Since these ACCs are always found at the same frequencies, they can be readily located and monitored by the mobile stations.
For example, when in an idle state (i.e., switched on but not making or receiving a call), a mobile station tunes in to, and then regularly monitors the strongest control channel (generally, the control channel of the cell in which the mobile station is located at that moment) and may receive or initiate a call through the corresponding base station. When moving between cells while in the idle state, the mobile station will eventually “lose” radio connection on the control channel of the “old” cell and tune to the control channel of the “new” cell. The initial tuning and subsequent re-tuning to control channels are both accomplished automatically by scanning all the available control channels at their known frequencies to find the “best” control channel. When a control channel with good reception quality is found, the mobile station remains tuned to this channel until the quality deteriorates again. In this way, mobile stations stay “in touch” with the system.
While in the idle state, a mobile station must monitor the control channel for paging messages addressed to it. For example, when an ordinary telephone (land-line) subscriber calls a mobile subscriber, the call is directed from the public switched telephone network (PSTN) to a mobile switching center (MSC) that analyzes the dialed number. If the dialed number is validated, the MSC requests some or all of a number of radio base stations to page the called mobile station by transmitting over their respective control channels paging messages that contain the mobile identification number (MIN) of the called mobile station. Each idle mobile station receiving a paging message compares the received MIN with its own stored MIN. T
Burns Doane Swecker & Mathis L.L.P.
Nguyen Lee
Nguyen Simon
Telefonaktiebolaget LM Ericsson (publ)
LandOfFree
Method and apparatus for saving current while performing... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for saving current while performing..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for saving current while performing... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2484799