ISM terminology
This pages gives a brief explanation of the most common terminologies used within wireless technology
ACP
The Adjacent Channel Power is a measure on how much of the transmitted power that appears in an adjacent channel relative to the signal channel. This defines how close two defined channels can be. The ACP is measured in dBc. (The "c" indicates that it is measured in dB with respect to the carrier). The ACP affects how narrow band the transmitter can be. The performance of the WNC transmitter unit is -46 dBc at 433MHz with 12.5 kHz channel spacing and -49 dBc at 868MHz with 25 kHz channel spacing.
ACR
Adjacent Channel Rejection is a special case of selectivity, where the unwanted signal is in the neighbouring channel. The ACR is measured in dB.
ASK
Amplitude Shift Keying modulation. Logic 1 and logic 0 are represented by two different signal amplitudes.
Bit synch offset
The maximum bit synch offset between receiver and transmitter allowed. Measured in % of the data rate. This figure is relevant only where a system is using radio link set up with transceivers from two different suppliers
Blocking
Same as selectivity, but normally used for situations where the unwanted signals are further away (in the frequency band) from the wanted signal. Blocking indicates for example how well the 868MHz transceiver can handle noise from the GSM network (900MHz). The blocking is measured in dB.
Carlson's rule
The Carlsons rule can be used as an approximate calculation of the BW needed at transceiver side (applies where FSK modulation is used only).
Signal BW = 2*fm + 2*freq deviation = baud rate + frequency separation
CCR
The Co-Channel Rejection is a special case of selectivity where the disturbing frequency is the same frequency/channel as the wanted signal. Example: For the WNC transceiver the wanted signal needs to be 11dB higher than the unwanted signal at the receiver side in order to detect the wanted signal correctly. The CCR is measured in dB.
dB
Decibel is the unit used to express the relative difference in power of intensity between two signals (radio, electric, or acoustic signals), and is equal to ten times the common logarithm of the ratio of the two levels.
Decibel is named after Alexander Graham Bell (one 10th of a Bel). Applied to increase or decrease in power levels (in Watts), the formula is dB=10*log(input signal/output signal)
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dBm
decibel below 1 milliwatt. A measurement of power in decibels using 1 milliwatt as the reference point. ( 0dBm = 1 mW, 3dBm = 2 mW, etc)
Diff. BPSK
Differentiated Binary PSK modulation, ie. 2PSK
Diff. QPSK
Diff. Quadrouple PSK modulation, ie. 4 PSK. One symbol creates two bits
FIFO
First in First out. This is the memory inside the transceiver where the data is stored on a first-in-first-out principle.
Filter bandwidth
Filter BW is the bandwidth needed at the receiver side in order to capture the wanted signal.
Filter BW = Signal BW + 4*crystal inaccuracy.
Frequency deviation
Frequency deviation = Frequency separation / 2 (Applies to FSK only)
Frequency separation
The distance in frequency between the signal frequency representing logic 0 and the signal frequency representing logic 1. (Applies to FSK only).
FSK
Frequency Shift Keying modulation. One frequency is representing logic 0 and another frequency representing logic 1.
ICR
The Image Channel Rejection is a special case of selectivity and indicates how well the receiver unit represses the image frequency. The ICR is measured in dB.
IF
Intermediate Frequency. This signal is generated inside the receiver and is the result of mixing the received signal with the LO signal. This is done in order to have a resulting signal that is closer to 0 frequency (than the originally received signal). The distance (in frequency) between the input signal and the LO is called the IF.
IIP3
IIP3 is the 3rd order Input Intercept Point and indicates how linear the receiver amplifier is. Consider the following situation: Two unwanted signals that are outside the receiver bandwidth will be suppressed due to the selectivity of the receiver, and as such will not cause a problem. However, the two unwanted signals generate 3rd order signals (eg. 2f1-f2) in the LNA of the receiver chip due to the non-linearity of the LNA (provided the frequency of the 3rd order signal is inside the receiver BW. This influences the maximum range (in addition to sensitivity and output power). The IIP3 is measured in dBm. The higher the value is, the better, as it means that the 3.order unwanted signal is repressed more. With a good IP3 level one can obtain a longer range before an external SAW filter is needed.
IIP3 = Jammer signal strength + IM/2
IM = Jammer signal strength - 3rd order signal strength
IM = Intermodulation signal strength
Example: A receiver with IIP3 of -15dB and a CCR of 11dB receives an unwanted signal which has a signal strength of -48dBm. The inter modulation signal is then at 66dB and the 3rd order signal is at -114 dBm (-48dBm -66 dB). Since the CCR is 11dB it means that the wanted signal must be 11dB stronger than the 3rd order signal, ie -103dBm.
Image frequency
The image frequency is an unwanted signal inside the receiver (that is created by the receiver itself) and is seen after the mixer. Problems may occur if there is an unwanted signal that accidentally is at fws - 2*(fws - fLO) = fws - 2*IF
ISM
ISM stands for "Industrial, Scientific, Medical". The ISM bands (433MHz and 868MHz in Europe, 915MHz in the US and 2,4GHz world wide) were originally defined and regulated for applications within these three areas. Even though the wireless technology and these frequency bands have been deployed in many other sectors, "ISM" is still used as the common term for the license free bands.
LNA
Low Noise Amplifier. The LNA is a unit within the radio receiver that amplifies the incoming signal. The amplification is indicated in dB.
LO
LO is normally the abbreviation for the Local Oscillator inside the receiver. The higher the resolution of the LO is, the better. (The transceiver in the WNC system has a LO resolution of 300 Hz for 433MHz and 600Hz for 868 MHz).
OOK
On Off Keying modulation. Subset of ASK where logic 0 is represented by 0 (zero) amplitude and logic 1 is represented by a signal amplitude that is not 0.
Output power tolerance
The output power tolerance is measured in dB and indicates how the maximum output power varies with temperature and supply voltage.
PLL lock time
The time it takes for the transceiver unit to switch between receive and transmit mode. The PLL lock time depends on the data rate and is measured in us.
PSK
Phase Shift Keying modulation. Logic 1 and logic 0 are represented by different phase shifts in the signal.
Range
The range is measured in meters and is the maximum distance between the transmitter and receiver (or two transceivers).
Receiver
The receiver is the radio unit that is receiving the radio signal
Saturation
The saturation level is measured in dBm and describes the maximum input signal strength a receiver is able to tolerate before the signal becomes distorted. If the saturation level is lower than the maximum output level from the transmitter, this will give a minimum range between the transmitter and receiver, which has to be respected in order to avoid distortion. WNC uses a transceiver, which has a saturation level higher than the output level, and therefore there is no minimum range (ie the transmitter and receiver can be placed next to one another).
Selectivity
The selectivity is measured in dB and expresses how much other (not wanted) signals are repressed by the receiver unit. In other words, the selectivity indicates how much larger an unwanted signal can be with respect to the wanted signal. The higher the value is, the better, as this means that the transceiver can work in a noisier environment.
Sensitivity
The sensitivity of a receiver is measured in dBm and is the minimum signal strength that can be detected correctly by the receiver unit. The lower the sensitivity is, the better, as it means the receiver will be able to detect and receive correctly a very weak signal, which again means that the maximum distance between the transmitter and receiver can be longer.
Signal Bandwidth
The bandwidth of the radio signal is determined by the phase noise generated by the transmitter, which again affects the ACP.
Transceiver
A unit that operates both as a transmitter and receiver. Transceivers are used to establish a 2-way communication.
Transmitter
The transmitter is the unit sending the radio signal.
4FSK
FSK modulation with 4 frequencies rather than 2. In 4FSK one symbol creates two bits.