This invention relates in general to radio communications and more particularly to speech and channel coding techniques associated with a digital two-way radio.
In current two-way digital radio communications, a speech call can suddenly be terminated or “dropped” when a user's transmitted signal travels beyond a certain range. In a single site environment these drops are particularly bothersome for users accustomed to analog radio performance. Analog radio users are accustomed to listening to the audio signal until significant degradation in the audio quality occurs. This type of performance does not typically occur in digital communications since the communication is dropped.
While the audio output quality of today's digital two-way radios remains fairly consistent throughout a call, audible clicks are typically heard if the radio user is about to cross a certain signal threshold range. Analog radio quality, on the other hand, gradually improves as a user approaches the transmitting device. Conversely, it gradually degrades as the user moves a further distance away from the transmitting station. Current coding schemes and scaling techniques tend to be better suited to improving audio quality in a cellular protocol environment than those related to two-way radio protocol.
Thus, range extension and audio quality are particularly important when dealing with half-duplex two-way communication. Accordingly, there is a need for an improved range extension scheme for two-radio radio communications devices operating using a digital half-duplex two-way radio protocol wherein the received audio quality is altered based upon the signal level of the transmitting station.
The features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in conjunction with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which:
While the specification concludes with claims defining the features of the invention that are regarded as novel, it is believed that the invention will be better understood from a consideration of the following description in conjunction with the drawing figures, in which like reference numerals are carried forward.
In accordance with the present invention, there is described herein a means and method for extending audio quality and range in a digital two-way radio communication device. As seen in
Additionally, the receiving radio 303 includes a receive path 304 that processes an incoming RF signal 332 through a demodulator 316, a variable rate channel decoder 318 and a variable rate speech decoder 320 to generate speech output 334. The receiving radio 303 further includes a controller 336 and a transmitter 328. The transmitter 328 includes a reverse channel data decoder 338 and a modulator 340. An antenna switch 314 is also used to switch between receive and transmit modes.
In accordance with the preferred embodiment of the invention, the receiving radio 303 conveys and/or transmits BER data to the main transmitting radio 301 along with desired predetermined audio quality and range parameters. The transmitting radio 301 processes the BER information and transmits adjusted or modified parameters to the receiving radio 303. These adjusted parameters are sent in order to adjust and control the functionality of the variable rate channel decoder 318 and the variable rate speech decoder 320 of the receiving radio 303. At the same time receiver 303 has capability to identify what has changed or has remained unchanged within the received frame.
In accordance with the present invention, the variable bit rate aspect of the channel decoder 318, channel encoder 308, speech decoder 320, and speech coder 306 provides scalability and dynamic control to these devices. Thus, in accordance with the present invention, receiving radio 303 can be viewed as comprising a scalable digital vocoder 320 and a scalable channel decoder 318. Likewise, in accordance with the present invention, digital radio 301 can be viewed as comprising a dynamic digital vocoder 306 and a dynamic channel coder 308. The supporting protocol provided via controller 322 provides predetermined digital audio quality and predetermined audio output bit rate information at regular intervals to control the scalable digital vocoder 306 and the scalable channel coder 308. The scalability aspect of both of these coders allows the digital audio quality to be controlled such that it can be easily varied linearly with bit error rate (BER). Since the BER generally corresponds to the distance the receiving station is from the transmitting station, this achieves the desired behavior as seen in
To achieve the desired linear performance, predetermined digital audio quality and predetermined audio output bit rate information are transmitted to the coders 306, 308 via extra bits allocated in a reverse channel decoder 328. For the first embodiment of the invention, the digital two-way protocol originating from controller 336 utilizes a reverse channel to transmit relevant system parameters from the receiving radio 303 to the main transmitting radio 301 at regular intervals. In this case, the reverse channel control protocol includes a sufficient number of bits to transmit the bit rate related information regularly.
As seen in
Thus,
Referring now to
In accordance with yet a third embodiment of the invention, the BER is used to determine the output source coding bit rate (CBR). The output bit rate of the variable rate speech coder and variable rate channel coder are controlled on the basis of message error rate (MER) generated from the BER of the received signal. Quality requirement information is transmitted back to the transmitting device so that the transmitting device can generate scalable speech coder frames and channel coder frames.
Since the modulation scheme and allocated bandwidth are limited and fixed, the total gross bit rate 606 as seen in
Thus, the third embodiment of the invention achieves the outcome described in the second embodiment without the use of additional bits. In this solution, the existing method of BER transmission and reception is modified. Typically, the main transmitter uses the BER related information to control the output RF-power. In accordance with the third embodiment, the main transmitter is modified so that BER related information can be used for either power control or for controlling the output source coding bit rate. Thus, in accordance with the third embodiment, the main transmitter receives signaling frames containing a bit error rate (BER) in reverse channel and utilizes the BER for selectively controlling a radio frequency (RF) power output and source coding bit rate. The bit error rate value is mapped to generate speech coder and channel coder steps. The transmitter then adjusts the channel coding and speech coding rate according to the received bit rate. The receiver then predicts the channel coding and speech coding format from the BER it has sent in the previous reverse signaling frame.
In still yet a fourth embodiment, instead of sending BER, received audio quality measurements are sent on the reverse channel. The audio quality can be computed at the receiving radio 303 by determining the audio frames that need repeating at the decoder 318 or it can be computed from the major errors in the decoder data frame. Thus, in accordance with the fourth embodiment, the main transmitter 301 receives signaling frames containing audio quality information in a reverse channel and utilizes the audio quality measurements for source coding bit rate. The audio quality measurements are mapped to generate speech coder 306 and channel coder 308 steps. The transmitter path 302 of radio 301 then adjusts the channel coding and speech-coding rate according to the received bit rate. The receiver path 304 of radio 303 then predicts the channel coding and speech-coding format from the audio quality measurements it has sent in the previous reverse signaling frame.
The variable speech coder output bit rate is preferably scaled within a predetermined range, such as for example from 1 to 9 kilobits per second (KBPS) depending on system parameters such as available transmission bit rate. The dynamic channel coder or adaptive channel coder of the present invention adjusts the output bit rate according to the BER or MER or audio quality measurements. Those skilled in the art will recognize that different system requirements may require different scaling factors; however, the ability to dynamically scale the coding enables significant control over range and audio quality.
Accordingly, the present invention describes a variable bit rate vocoder and variable bit rate channel coder which is a novel improvement over the fixed bit rate vocoder and channel coder used presently within digital simplex communications devices. A digital radio formed in accordance with the present invetion can receive signaling frames containing a bit error rate (BER), or audio quality measurements with the receiver utilizing the BER or audio quality meassurements or selectively controlling a radio frequency (RF) power output and source coding bit rate for the digital radio. Moreover, by modifying the BER related algorithms to provide for variable bit rates, a new means of controlling FEC and speech coder rate formatting has been provided for improved audio quality and range. The coding schemes of the present invention provide a dynamic scaling approach for two-way digital radio designs. Existing digital protocols do not dynamically scale the vocoder output rate or the channel coder output rate. By utilizing dynamic scaling approach such as linear or stepped the audio quality and range of digital two-way radio is greatly improved.
While the preferred embodiments of the invention have been illustrated and described, it will be clear that the invention is not so limited. Numerous modifications, changes, variations, substitutions and equivalents will occur to those skilled in the art without departing from the spirit and scope of the present invention as defined by the appended claims.