It addresses two of the primary benefits delivered by this technology: spectral efficiency and improved audio performance. This voice waveform is then sampled by an analog to digital converter. In typical radio applications, a bit sample is taken every 8 kHz, this produces a ,bps bits per second digital bitstream, which contains far too much information to send over a Therefore some form of compression is required.
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Figure Transmit Audio Sensitivity November, 14 System Feature Overview The flat audio response of digital is different from the traditional analog audio response. The traditional response is a linear response and the louder one speaks, then the louder the received volume.
Below this level, analog is quieter than digital. This is important to note as a system requiring MOTOTRBO to function as a digital radio and also as an analog radio during migration, may experience received audio level differences that are mode dependant. This could occur when scanning both digital and analog channels and the analog talker is located in a quiet environment such as an office.
In quiet environments many users tend to speak softly and therefore the input will fall below the equivalent response level of 98 dB SPL. Therefore, during the migration period, the analog response may be quieter than the digital response. This allows the user to assign voice or data traffic to either of the time slots independently. To the end user, this means they now have two voice or data channels that can be managed independently, instead of one.
These two logical channels two time slots can transmit and receive independently of each other. In this mode, repeaters across dispersed locations exchange voice and data packets over an IPv4-based back-end network. There are three main functions of this mode. November, System Feature Overview 15 2. The system only requires that one of the repeaters have a static IPv4 address, while the others may be dynamic. When a new call starts at one of the logical channel of a repeater, the repeater sends the call to all the repeaters and all these repeaters repeat the call on their corresponding logical channel.
This allows a radio in the coverage area of any repeater to participate in the call. Thus, the coverage area of an IP Site Connect system is the sum of the coverage areas of all the repeaters. However, note that an IP Site Connect configuration does not increase the capacity i. The capacity of one Wide Area Channel of an IP Site Connect system is approximately the same as that of a single repeater working in digital repeater mode.
Additionally, the radios are capable of automatically roaming from one site to another. If a customer has multiple MOTOTRBO systems working in digital repeater mode at dispersed sites and wants to convert them into an IP Site Connect system then the repeaters and the radios should be updated with new software and the repeaters need to be connected to an IPv4 based back-end network.
The tool called RDAC receives alarms from all the repeaters, helps in diagnosis of repeaters, and provides some controls over the repeaters In direct mode, receive and transmit functions are both carried out on the same physical channel i. On one direct Without a repeater in place to coordinate the time slot sequence among radios, only one radio can transmit at a time in order to guarantee transmissions do not overlap.
The mobile or portable radio user selects the mode of operation analog or digital , and physical and logical channel using his channel selector knob each channel selection position is configured for a particular call type on either a digital channel that specifies both frequency and time slot, or an analog channel that specifies both frequency and 25kHz or Radio channels are either analog or digital.
This is configured by the CPS. The radio can scan between analog and digital channels. The repeater does not block or deny any channel access from radios on its system, but will not repeat transmissions from another system.
In the configuration software, channel access is referred to as the Admit Criteria. Channel access methods must be specified for each channel in the radio CPS. All these channel access options govern how standard group voice calls and private calls access the system.
Not all transmission types utilize these settings. For example, emergency voice calls always operate impolitely. This gives emergency voice calls a slightly higher priority over existing traffic on the channel. Data calls are always polite. Since a data call can be queued and retried, its priority is considered lower than voice. Control messages used for signaling features are also always polite. The exception is the emergency alarm.
Emergency alarms are sent with a mix of impolite and polite channel access, in order to optimize the likelihood of successful transmission. When operating in IP Site Connect mode, the repeaters also check the channel for interference before transmitting.
This is required since even though the source radio checks the channel at one site, it does not mean there is no interference at another site. Therefore, a repeater will check for over the air interference before waking up and transmitting. The repeater always acts with an Admit Criteria of Channel Free and has a configurable signal strength threshold. Note that although one site may be busy, the other non-busy sites will continue with the call.
However, on a digital repeater channel, the radio checks if the repeater is hibernating. Transmission will not proceed, if the repeater is hibernating and the radio is unable to wake it. This causes RF contention at the target.
When RF contention occurs between digital transmissions, it is impossible to predict which signal is usable. If one transmission is much stronger than the other, it is received instead of the weaker signal. But in most cases, the two transmissions on the same frequency and time slot results in both transmissions being unusable.
Thus, it is recommended that only disciplined users are granted the right to use impolite operation. Further, those impolite users are encouraged to utilize the busy channel LED on their radio to determine, if the channel is idle prior to transmitting.
When operating in IP Site Connect mode, it is important to understand that impolite channel access only occurs at the local site. If the original source of the call is at a different site from the interrupting radio, the original call continues at all other sites except where the interrupting radio is located.
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