ADJACENT CHANNEL POWER RATIO

ACP measurements have been performed for many years. Originally, ACP measurements were used for narrowband analog modulated signals and measured the ratio of the upper and lower channels to the total power transmitted. The total power transmitted was defined as the carrier plus the majority of power in the upper and lower channels. Today, an ACP measurement is defined as the ratio of one or more upper and lower intervals of power to the total carrier power across the bandwidth of the channel.

Cellular communications systems have relied on ACP measurements to ensure that power radiated into an adjacent channel is limited—to ensure that the signal-to-noise ratio (SNR) in the adjacent channel does not interfere with communications in that channel. Cellular standards such a W-CDMA, cdma2000, and LTE all have defined methods and limits for ACP measurements. These standards go even further and even provide more descriptive names for ACP measurements. For example, cdma2000 adopted Adjacent Channel Power Ratio (ACPR) and W-CDMA adopted Adjacent Channel Leakage Ratio (ACLR) as more specific names for their versions of ACP measurements. GSM and EDGE have similar requirements that use what are called Output RF Spectrum (ORFS) measurements to ensure that power radiated into adjacent channels does not exceed certain levels. Most modern spectrum analyzers have programmed, predefined settings for various standards that allow for quick measurement setups.

For narrowband analog modulated signals, the phase noise present in the local oscillator (LO) accounted for most of the power present in the adjacent channels in these systems. Today, with the introduction of wide-bandwidth signals, the power in the adjacent channel(s) can potentially be from a combination of several factors, including phase noise, intermodulation distortion (IMD), and the noise floor of the system. Similarly, these factors influence the dynamic range a spectrum analyzer can achieve in making an ACP measurement.

For many of the current and future transmission standards (IS-95 CDMA, WCDMA and variants, IS-54 NADC,…), ACPR (sometimes also termed adjacent channel leakage ratio-ACLR) is an important test parameter for characterizing the distortion of subsystems and the likelihood that a given system may cause interference with a neighboring radio. Since this distortion mechanism requires a non-linearity, the most important subassembly to check is one of the least linear: the power amplifier. As a result, many power amplifier test systems must incorporate provisions to measure this quantity.

ACPR and Intermodulation Distortion (IMD)Even in early radio systems, the interfering effects of an active neighboring channel in mildly non-linear communications systems were well known. In these simpler modulation schemes, the use of two sinusoids to represent two active channels was considered adequate. The third-order product of these two tones (e.g., [2]) could land in a neighboring channel bandwidth thus causing interference. This was the beginning of two-tone intermodulation analysis. As the modulation becomes more complex, it becomes less obvious that the sinusoidal representation will adequately simulate the problem

The 3rd order IMD product is usually defined as the ratio of the power in one of the third-order tones to that in one of the main tones. ACPR is defined as the ratio of power in a bandwidth away from the main signal (the distortion product) to the power in a bandwidth within the main signal. This statement is intentionally vague since the bandwidths and locations are functions of the standards being employed. Alternate channel power ratio is also sometimes defined and it refers to the ratio of power in a bandwidth two channels away from the main

signal to the power in some bandwidth within the main signal. In terms of the IMD measurements, a 5 th order product (or some combination of higher order products) may correspond to the alternate channel power ratio.Because of the requirement for a modulated signal and the increased complexity in accurately measuring power over a precisely defined larger bandwidth, it has long been desired to avoid the direct measurement of ACPR and perhaps use IMD as a surrogate measurement. While in principle this is possible (perhaps using higher order IMD products) and is used in many cases, the correlation can be difficult since the relationship depends on the details of the amplifier topology as well as the modulated waveform being used (e.g., [3]-[6]). Thus in many cases, the true ACPR measurement must be performed.

In the discussions held on adjacent channel performance in ETSI, ARIB, ITU, 3GPP, etc. there has been some confusion regarding the terms used. Especially the acronym “ACP” seems to have different meanings depending on the context. WG4 has found it necessary to define three terms relating to adjacent channel performance, one to use for simulations, one for transmitter performance requirements and one for receiver performance requirements. Each term can be defined for any frequency offset. Thus “Adjacent Channel” may refer to not only the channel closest to the assigned channel, but also the 2nd Adjacent Channel, etc.

2.1.1 Adjacent channel performance in simulationsIn a system performance simulation where it is assumed that the transmitter and receiver use RF carriers that are adjacent, an assumption has to be made of how much power is leaking from the transmitter to the receiver on the adjacent channel. This adjacent channel interference power occurs because of both transmitter imperfections (transmitter mask) and receiver imperfections (non-ideal receiver filter). In a system simulation, the reason for the interference is irrelevant, it is the amount of interference that is interesting. This can be expressed as the ratio of the total transmitted power to the interference power affecting the receiver. This definition seems to be the one used in all system simulations presented to ETSI by different contributors, but it has been named differently (ACP, ACI, etc.). For simulation purposes, the following definition is proposed:

Adjacent Channel Interference power Ratio, ACIR = The ratio of the total power transmitted from a source (base station or UE) to the total interference power affecting a victim receiver, resulting from both transmitter and receiver imperfections.

2.1.2 Transmitter adjacent channel performanceMainly because of transmitter non-linearities, the spectrum mask from transmitter will leak into adjacent channels. This is a very important system parameter, since it is essential for the co-existence performance of systems on adjacent channels. It is also one of the most important design parameters for transmitters, since a too strict requirement on adjacent channel leakage can restrict the implementation of efficient and low complexity transmitters (especially for UE). The used term in ETSI and ARIB has previously been ACP or ACPR, but with unclear definition as to what is intended.

The following definition is proposed. The term and intention is identical to the one propose in ITU IMT.RKEY.

Adjacent Channel Leakage power Ratio, ACLR = The ratio of the transmitted power to the power measured after a receiver filter in the adjacent RF channel. Both the transmitted power and the received power are measured within a filter response that is nominally rectangular, with a noise power bandwidth equal to the chip rate.

2.1.3 Receiver adjacent channel performanceThe receiver will have additional interference from the adjacent channel, since the receiver filter cannot be ideal, i.e. not “nominally rectangular” as proposed in the definition of ACLR. The filter will have side lobes in the adjacent channel, causing the power from the main lobe of the transmitted interference source to affect receiver performance. For simulations and receiver design purposes, it is the receiver filter’s suppression of the main lobe of the transmitted signal in the adjacent channel that is of interest. This includes the RF filter suppression of the interference, but not the receiver processing gain. The following definition is proposed:

Adjacent Channel Selectivity, ACS: Adjacent Channel Selectivity is a measure of a receiver’s ability to receive a signal at its assigned channel frequency in the presence of a modulated signal in the adjacent channel. ACS is the ratio of the receiver filter attenuation on the assigned channel frequency to the receiver filter attenuation on the adjacent channel frequency.

2.1.4 Relation between ACIR, ACLR and ACSWith the above definitions, it is clear that the ACIR (total interference between adjacent channels) will depend solely on the ACLR and ACS performance numbers. All three are power ratios and the relation between them is

ACIR≌ 11

ACLR+

1ACS

In the uplink, the limiting design factor is the UE transmitter, which will dominate the uplink interference. The reason is that ACLRUE << ACSBS , which implies that uplink ACIR ACLRUE . Thus, in an uplink simulation, it is essentially the UE ACLR performance that is simulated.In the downlink, the limiting design factor is the UE receiver, which will dominate the downlink interference. The reason is that ACSUE << ACLRBS , which implies that downlink ACIR ACSUE . A downlink simulation will thus essentially be a simulation of UE ACS performance.

ADJACENT CHANNEL INTERFERENCE RATIO

Adjacent Channel Inetreference Ratio is teh ratio of wanted power to the interference power from the adjacent channels.

ADJACENT CHANNEL LEAKAGE RATIO

ACLR ids the measure of transmitted performsnce for WCDMA. It is defined as the ratio of the transmitted power to the power measure dafter the receiver filter in the adjacent RF channel. This is what was formely called Adjacent Channel Power Ratio. ACLR is specified in the 3GPP WCDMA standard.

ADJACENT CHANNEL POWER RATIO

ACPR is a measurement of the amount of interference or power in the adjacent frequency channel . ACPR is usally defined as the ratio of average power in the adjacent frequency chasnnel (or offset) to the average ower in the transmitted frequency channel. It is critical measurement fir the CDMA transmitters and their components.it describes the amount of distortion generated dueto nonlinearities in RF components. The ACPR is not the part of the cdmaOne standard.

ADJACENT CHANNEL SELECTIVITY

ACS is the measurement of receiver’s ability to process a desired signal while rejecting a strong signal in an adjacent frequency channel. ACS is defined as the ratio of the receiver filter attenuation on the assigned channel frequency to the receiver filter attenuation oon the adjacent channel frequency