CDMA spectral efficiency refers to the system spectral efficiency in bit/s/Hz/site or Erlang/MHz/site that can be achieved in a certain CDMA based wireless communication system. CDMA techniques (also known as spread spectrum) are characterized by a very low link spectral efficiency in (bit/s)/Hz as compared to non-spread spectrum systems, but a comparable system spectral efficiency.
The system spectral efficiency can be improved by radio resource management techniques, resulting in that a higher number of simultaneous calls and higher data rates can be achieved without adding more radio spectrum or more base station sites. This article is about radio resource management specifically for direct-sequence spread spectrum (DS-CDMA) based cellular systems.
Examples of DS-CDMA based cellular systems are:
The terminology used in this article is firstly based on 3GPP2 standards.
CDMA is not expected to be used in 4G systems, and is not used in pre-4G systems such as LTE and WiMAX, but is about to be supplemented by more spectral efficient frequency-domain equalization (FDE) techniques such as OFDMA.
The aim of improving system spectral efficiency is to use limited radio spectrum resources and radio network infrastructure as efficiently as possible. The objective of radio-resource management is typically to maximize the system spectral efficiency under constraint that the grade of service should be above a certain level. This involves covering a certain area and avoiding outage due to co-channel interference, noise, attenuation caused by long distances, fading caused by shadowing and multipath, Doppler shift and other forms of distortion. The grade of service is also affected by blocking due to admission control, scheduling starvation or inability to guarantee quality of service that is requested by the users.
There are many ways of increasing system spectral efficiency. These include techniques to be implemented at the handset level or at the network level. They include network optimization and vocoder rate encapsulation. Issues faced while deploying these techniques are the cost, upgrade requirements, hardware and software changes (which includes cell phone compatibility corresponding to the changes) to be made and the agreements to be approved from the telecommunication department.
Due to its large transmission power, the Common pilot channel (CPICH) probably consumes 15 to 20 percentage of the forward as well as the reverse link capacity[ citation needed ]. Co-channel interference is obvious. It is hence important to initialize interference cancellation techniques such as pilot interference cancellation (PIC) and forward link interference cancellation (FLIC) together in the network. Quasi-linear interference cancellation (QLIC) is a technique used for both FLIC and PIC.
Along with the forward link, reverse link interference cancellation is also important. Interference will be reduced and the mobiles will have to transmit less power to get the line of sight [ clarification needed ] with the base station which will in turn increase the battery life of the mobile.
The 1/8 rate gating on the reverse fundamental channel (R-FCH) is the method used for gated transmission in a CDMA communication system. A mobile station (mobile phone) in the CDMA communication system transmits a reverse pilot signal at a reverse gating rate which is different from a forward gating rate in a gated mode, and a base station transmits a forward pilot signal at the forward gating rate different from the forward gating rate in a gated mode.
When the duty cycle is 1/8, only 1/8 of the whole power control groups in one frame are transmitted. This behavior is not present in any other CDMA modes.
Another CDMA invention to provide a device and technique for improving a downlink phone capacity and receiving performance by gating an uplink DPCCH signal in a partial period of the power control group in a mobile communication system. The test set's support for the R-FCH gating mode is disabled (off) by default.
If the test set's R-FCH gating mode is enabled (on) and the mobile station (MS) supports the gating mode, the MS will gate the R-FCH/R-Pilot Channel when transmitting at 1/8 rate. This will save around 75%[ citation needed ] of the power on an average on reverse channels.
| Radio Config | Programming mnemonic | C.S0002-A Standard | Test Mode in TIA/EIA-98-E | |
|---|---|---|---|---|
| Forward Traffic Channel Radio Configuration | Reverse Traffic Channel Radio Configuration | |||
| (Fwd1, Rvs1) | F1R1 | RC1 | RC1 | 1 |
| (Fwd2, Rvs2) | F2R2 | RC2 | RC2 | 2 |
| (Fwd3, Rvs3) | F3R3 | RC3 | RC3 | 3 |
| (Fwd4, Rvs3) | F4R3 | RC4 | RC3 | 4 |
| (Fwd5, Rvs4) | F5R4 | RC5 | RC4 | 5 |
The CDMA radio configuration is defined as a combination of forward and reverse traffic channel transmission formats that are characterized by physical layer parameters such as data rates, error-correction codes, modulation characteristics, and spreading factors. The traffic channel may consist of one or more code channels such as fundamental channels and supplemental channels.
The forward link of a 3G code-division multiple-access (CDMA) system may become a limiting factor when the number of users increases maximal capacity.
The conventional channelization code, Walsh code does not have enough available bits to cope with maximal use. Therefore, the quasi-orthogonal function (QOF), which can process optimal cross-correlation with Walsh code has been used as a method to get around the limitations of the Walsh Codes.
To enhance the overall capacity in such scenarios, alternative sets of orthogonal functions called the quasi-orthogonal functions (QOF), which possess optimal minimax cross correlation with Walsh code sets of variable length, have been incorporated in IS-2000.
This method uses aggregation of multiple quasi-orthogonal functions with a smaller constellation alphabet size for a single user with a joint multi-channel detector. This method is compared with the alternative method for enhancing the maximum throughput using aggregation of a smaller number of Walsh functions, but with a higher constellation alphabet size (multi-level modulation).
There have been many industrial and academic discussions on the trade-offs with respect to better methods for increasing capacity in IS-2000/3G systems. QOF introduces high amount of interference in the network channels, thus limiting its benefits.
There are some places where the utilization of the site is very high and excess softer handoffs occur. For such sites, a 6-sector antenna is one of the solutions, as it provides greater coverage granularity than the traditional 3-sector antenna. Instead of 1 BTS, 2 BTS are used and hence the antennas can be separated from each other by 60 degrees instead of 120 degrees.
Antenna diversity, also known as space diversity (micro-diversity as well as macro-diversity, i.e. soft handover, see below), is any one of several wireless diversity schemes that use two or more antennas to improve the quality and reliability of a wireless link.
Often, especially in urban and indoor environments, there is not a clear line-of-sight (LOS) between transmitter and receiver. Instead the signal is reflected along multiple paths before finally being received. Each of these bounces can introduce phase shifts, time delays, attenuations, and even distortions that can destructively interfere with one another at the aperture of the receiving antenna.
Antenna diversity is especially effective at mitigating these multipath propagation situations. This is because multiple antennas afford a receiver several observations of the same signal. Each antenna will experience a different interference environment. Thus, if one antenna is experiencing a deep fade, it is likely that another has a sufficient signal.
Collectively such a system can provide a robust link. While this is primarily seen in receiving systems (diversity reception), the analog has also proven valuable for transmitting systems (transmit diversity) as well.
Inherently an antenna diversity scheme requires additional hardware and integration versus a single antenna system but due to the commonality of the signal paths a fair amount of circuitry can be shared.
With multiple signals there is a greater processing demand placed on the receiver, which can lead to tighter design requirements of the base station. Typically, however, signal reliability is paramount and using multiple antennas is an effective way to decrease the number of drop-outs and lost connections.
Qualcomm's fourth generation vocoder (4GV) is a suite of voice speech codecs expected to be used in future 4G networks as well CDMA networks, that allows the network operators to dynamically prioritize voice quality to increase network capacity while maintaining voice quality. Currently, the 4GV suite offers EVRC-B and EVRC-WB.
Enhanced Variable Rate Codec B (EVRC-B) is a speech codec used by CDMA networks. EVRC-B is an enhancement to EVRC and compresses each 20 milliseconds of 8000 Hz, 16-bit sampled speech input into output frames of one of the four different sizes: Rate 1 - 171 bits, Rate 1/2 - 80 bits, Rate 1/4 - 40 bits, Rate 1/8 - 16 bits.
In addition, there are two zero bit codec frame types: null frames and erasure frames, similar to EVRC. One significant enhancement in EVRC-B is the use of 1/4 rate frames that were not used in EVRC. This provides lower average data rates (ADRs) compared to EVRC, for a given voice quality. The new 4GV Codecs used in CDMA2000 are based on EVRC-B. 4GV is designed to allow service providers to dynamically prioritize voice capacity on their network as required.
The Enhanced Variable Rate Codec (EVRC) is a speech codec used for cellular telephony in cdma2000 systems. EVRC provides excellent[ citation needed ] speech quality using variable rate coding with 3 possible rates, 8.55, 4.0 and 0.8 kbit/s. However, the Quality of Service (QoS) in cdma2000 systems can significantly benefit from a codec which allows tradeoffs between voice quality and network capacity, which cannot be achieved efficiently with the EVRC.
Higher combined Ec/Io, lower traffic channel Ec/Io is required and more BTS power is conserved. Ec/Io is a notation used to represent a dimensionless ratio of the average power of a channel, typically the pilot channel, to the total signal power. It is expressed in dB.
There are some remote places where BTS signal penetrates but reverse link of mobile cannot reach back to the base station. Solution is like reducing base station antenna height, down tilt, select lower gains, etc.
There are some areas with more soft handoff than necessary. The handoff parameters has to be reduced to save the base station power. Set higher values of T_ADD and T_DROP, and check the sector coverage should not be too high or too low.
For best quality decrease the FPCH (Forward Pilot Channel) and FER (Frame Error Rate) settings to 1% and for increase the capacity of highly loaded sites, increase the settings of these parameters to more than 3%.
Some sites have very low utilization and due to coverage issue, a new site is required in nearby areas. Instead of a new site, a Cellular repeater can be used effectively to provide coverage solutions.
Code-division multiple access (CDMA) is a channel access method used by various radio communication technologies. CDMA is an example of multiple access, where several transmitters can send information simultaneously over a single communication channel. This allows several users to share a band of frequencies. To permit this without undue interference between the users, CDMA employs spread spectrum technology and a special coding scheme.
In telecommunications, orthogonal frequency-division multiplexing (OFDM) is a type of digital transmission used in digital modulation for encoding digital (binary) data on multiple carrier frequencies. OFDM has developed into a popular scheme for wideband digital communication, used in applications such as digital television and audio broadcasting, DSL internet access, wireless networks, power line networks, and 4G/5G mobile communications.
Speech coding is an application of data compression to digital audio signals containing speech. Speech coding uses speech-specific parameter estimation using audio signal processing techniques to model the speech signal, combined with generic data compression algorithms to represent the resulting modeled parameters in a compact bitstream.
In telecommunications and computer networking, multiplexing is a method by which multiple analog or digital signals are combined into one signal over a shared medium. The aim is to share a scarce resource - a physical transmission medium. For example, in telecommunications, several telephone calls may be carried using one wire. Multiplexing originated in telegraphy in the 1870s, and is now widely applied in communications. In telephony, George Owen Squier is credited with the development of telephone carrier multiplexing in 1910.
In telecommunications and computer networks, a channel access method or multiple access method allows more than two terminals connected to the same transmission medium to transmit over it and to share its capacity. Examples of shared physical media are wireless networks, bus networks, ring networks and point-to-point links operating in half-duplex mode.
Interim Standard 95 (IS-95) was the first ever CDMA-based digital cellular technology. It was developed by Qualcomm and later adopted as a standard by the Telecommunications Industry Association in TIA/EIA/IS-95 release published in 1995. The proprietary name for IS-95 is cdmaOne.
IS-54 and IS-136 are second-generation (2G) mobile phone systems, known as Digital AMPS (D-AMPS), and a further development of the North American 1G mobile system Advanced Mobile Phone System (AMPS). It was once prevalent throughout the Americas, particularly in the United States and Canada since the first commercial network was deployed in 1993. D-AMPS is considered end-of-life, and existing networks have mostly been replaced by GSM/GPRS or CDMA2000 technologies.
Evolution-Data Optimized is a telecommunications standard for the wireless transmission of data through radio signals, typically for broadband Internet access. EV-DO is an evolution of the CDMA2000 (IS-2000) standard which supports high data rates and can be deployed alongside a wireless carrier's voice services. It uses advanced multiplexing techniques including code-division multiple access (CDMA) as well as time-division multiplexing (TDM) to maximize throughput. It is a part of the CDMA2000 family of standards and has been adopted by many mobile phone service providers around the world particularly those previously employing CDMA networks. It is also used on the Globalstar satellite phone network.
Qualcomm code-excited linear prediction (QCELP), also known as Qualcomm PureVoice, is a speech codec developed in 1994 by Qualcomm to increase the speech quality of the IS-96A codec earlier used in CDMA networks. It was later replaced with EVRC since it provides better speech quality with fewer bits. The two versions, QCELP8 and QCELP13, operate at 8 and 13 kilobits per second (Kbit/s) respectively.
This article discusses the mobile cellular network aspect of teletraffic measurements. Mobile radio networks have traffic issues that do not arise in connection with the fixed line PSTN. Important aspects of cellular traffic include: quality of service targets, traffic capacity and cell size, spectral efficiency and sectorization, traffic capacity versus coverage, and channel holding time analysis.
Spectral efficiency, spectrum efficiency or bandwidth efficiency refers to the information rate that can be transmitted over a given bandwidth in a specific communication system. It is a measure of how efficiently a limited frequency spectrum is utilized by the physical layer protocol, and sometimes by the medium access control.
Enhanced Variable Rate Codec B (EVRC-B) is a speech codec used by CDMA networks. EVRC-B is an enhancement to EVRC and compresses each 20 milliseconds of 8000 Hz, 16-bit sampled speech input into output frames of one of the four different sizes: Rate 1 - 171 bits, Rate 1/2 - 80 bits, Rate 1/4 - 40 bits, Rate 1/8 - 16 bits.
This is a comparison of standards of mobile phones. A new generation of cellular standards has appeared approximately every tenth year since 1G systems were introduced in 1979 and the early to mid-1980s.
Dynamic Single Frequency Networks (DSFN) is a transmitter macrodiversity technique for OFDM based cellular networks.
In telecommunications, a diversity scheme refers to a method for improving the reliability of a message signal by using two or more communication channels with different characteristics. Diversity is mainly used in radio communication and is a common technique for combatting fading and co-channel interference and avoiding error bursts. It is based on the fact that individual channels experience fades and interference at different, random times, i.e, they are at least partly independent. Multiple versions of the same signal may be transmitted and/or received and combined in the receiver. Alternatively, a redundant forward error correction code may be added and different parts of the message transmitted over different channels. Diversity techniques may exploit the multipath propagation, resulting in a diversity gain, often measured in decibels.
Radio resource management (RRM) is the system level management of co-channel interference, radio resources, and other radio transmission characteristics in wireless communication systems, for example cellular networks, wireless local area networks, wireless sensor systems, and radio broadcasting networks. RRM involves strategies and algorithms for controlling parameters such as transmit power, user allocation, beamforming, data rates, handover criteria, modulation scheme, error coding scheme, etc. The objective is to utilize the limited radio-frequency spectrum resources and radio network infrastructure as efficiently as possible.
In radio, cooperative multiple-input multiple-output is a technology that can effectively exploit the spatial domain of mobile fading channels to bring significant performance improvements to wireless communication systems. It is also called network MIMO, distributed MIMO, virtual MIMO, and virtual antenna arrays.
WiMAX MIMO refers to the use of Multiple-input multiple-output communications (MIMO) technology on WiMAX, which is the technology brand name for the implementation of the standard IEEE 802.16.
In radio, multiple-input and multiple-output (MIMO) is a method for multiplying the capacity of a radio link using multiple transmission and receiving antennas to exploit multipath propagation. MIMO has become an essential element of wireless communication standards including IEEE 802.11n, IEEE 802.11ac, HSPA+ (3G), WiMAX, and Long Term Evolution (LTE). More recently, MIMO has been applied to power-line communication for three-wire installations as part of the ITU G.hn standard and of the HomePlug AV2 specification.
Multiple-input, multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) is the dominant air interface for 4G and 5G broadband wireless communications. It combines multiple-input, multiple-output (MIMO) technology, which multiplies capacity by transmitting different signals over multiple antennas, and orthogonal frequency-division multiplexing (OFDM), which divides a radio channel into a large number of closely spaced subchannels to provide more reliable communications at high speeds. Research conducted during the mid-1990s showed that while MIMO can be used with other popular air interfaces such as time-division multiple access (TDMA) and code-division multiple access (CDMA), the combination of MIMO and OFDM is most practical at higher data rates.
