Computer Communications
Volume 23, Issues 5–6,
1 March 2000
, Pages 476-482
Author links open overlay panel,
Abstract
Global System for Mobile Communications (GSM) supports full-rate and half-rate calls. In this paper, we propose analytical and simulation models to study the performance of four channel assignment schemes for GSM half-rate and full-rate traffic. Our study indicates that among the four schemes, the repacking scheme has the best performance for mixing half-rate and full-rate traffic. We also observe that good performance is expected if the standard derivation of the cell residence time for a mobile station is large.
Introduction
Global System for Mobile Communications (GSM) [1] is a standard adopted by cellular systems widely developed in Europe and Asia. In a GSM network, a mobile station (MS) initiates a communication session by making an access request to a base station (BS), if the MS is in the cell (the radio coverage area) of the BS. If no channel is available at that cell, the call is blocked. If the MS moves to another cell during the conversation, then the radio link to the old BS is disconnected and a radio link to the new BS is required to continue the conversation. This process is called handoff [2], [3]. If the new BS does not have any idle channel, the handoff call is dropped or forced to terminate. Handoff requests and new call requests compete for radio channels in a cell. Several channel assignment schemes [4] have been proposed to reduce call blocking and call dropping.
GSM combines time division multiple access (TDMA) and frequency division multiple access (FDMA) for radio channel allocation. In this approach, a frequency carrier is divided into eight time slots per frame, which are used to support speech and data transmission. GSM supports full-rate calls and half-rate calls. A full-rate call uses one time slot in every frame, while a half-rate call uses one time slot in every two frames. Once an MS initiates a full-rate (half-rate) call request, the MS will operate in full-rate (half-rate) mode until the call is terminated. A call may alternate between full-rate and half-rate channels [5]. Such an approach is not considered here. In this paper, mixing full- and half-rate calls in a frequency carrier result in eight full-rate calls, 16 half-rate calls, or any feasible combinations. To simplify the description, we view a GSM time slot as a “full” time slot that can be divided into two half time slots. Fig. 1 shows a feasible combination. In this figure, time slots 4 and 7 are idle. Time slots 1, 2 and 5 are occupied by full-rate calls F1, F2 and F3, respectively. Time slot 3 is occupied by two half-rate calls H2 and H3. Time slots 0 and 6 are occupied by half-rate calls H1 and H4, respectively. These two time slots are referred to as “partially occupied” time slots. The channel allocation strategies for incoming calls may significantly affect the performance. For example, if eight half-rate calls occupy eight different full time slots in a frequency carrier; that is, the eight time slots are partially occupied, then the next incoming full-rate call will be blocked. On the other hand, if these half-rate calls are packed into four full time slots, then the frequency carrier can accommodate four extra full-rate calls. In this paper, we evaluate four GSM channel assignment schemes described in Ref. [6]: random, repacking, fair-repacking and best-fit. These schemes are elaborated as follows.
Random: all full-rate and half-rate calls are assigned to any free time slots without any control.
Best-Fit: each incoming full-rate call is allocated an empty full time slot. A half-rate call is always assigned a partially occupied time slot that has already contained a half-rate call. If no such time slot exists, then an empty full time slot is assigned to the half-rate call. Note that when a half-rate call departs, it is possible that more than one partially occupied time slots exist.
Repacking: this scheme is similar to the best-fit scheme except that when a full-rate call arrives to a cell, the scheme repacks the half-rate calls if two partially occupied time slots exist. Repacking is achieved by intracell handoff technology.
Fair-Repacking: this scheme is a variation of the repacking scheme. The only difference between repacking and fair-repacking is that in fair-repacking, if only one half time slot is left in a cell, the next incoming half-rate calls will be blocked. In Ref. [6], the authors claimed that with fair-repacking, the blocking/force-termination probabilities of full- and half-rate calls are likely to be equal for mix traffic. Our study will indicate that when the number of channel in a cell is small, fair-repacking significantly degrades the performance of the full-rate calls without improving the half-rate call performance. On the other hand, the performance of fair-repacking is similar to repacking for a GSM cell with a large channel number. Since the implementation complexity for fair-repacking is higher than that for repacking, fair-repacking may not be appropriate for a practical GSM network.
The above four algorithms have been evaluated in Ref. [6] without considering the MS mobility. By accommodating the MS mobility, this paper proposes an analytical model for repacking and simulation models for the four schemes.
Section snippets
Input parameters and output measures
This section lists the input parameters and output measures used in this paper. The input parameters include
- •
λf (λh): the new full-rate (half-rate) call arrival rate to a cell
- •
1/μf (1/μh): the expected full-rate (half-rate) call holding time
- •
ηf (ηh): the full-rate (half-rate) MS mobility rate
- •
c: total number of time slots in a cell
The output measures include
- •
λh,f (λh,h): the handoff full-rate (half-rate) call arrival rate to a cell
- •
pf,f (pf,h): the force-termination probability for the full-rate
An analytical model for repacking
This section proposes an analytical model for the repacking scheme, which accommodates MS mobility. We assume that the full-rate (half-rate) call arrivals to a GSM cell form a Poisson process. Consider the timing diagram in Fig. 2. Let tci be the call holding time for type i call where i=f (full-rate) or h (half-rate), which is assumed to be exponentially distributed with the density functionand the mean call holding time is E[tci]=1/μi. The cell residence time of an
Discrete event simulation models
This section describes a discrete event simulation model for repacking, best-fit, fair-repacking and random. In our simulation experiments, the GSM network is configured with k2 BSs connected as a k×k wrapped mesh [10], where k=6 is found adequate to simulate a large-scale GSM network. We assume that an MS resides at a cell for a period, and then moves to one of the four neighboring cells with the same routing probability (i.e. 0.25). The full-rate (half-rate) call arrivals to each cell form a
Performance evaluation
This section investigates the performance of the four GSM channel assignment schemes based on the performance models developed in 3 An analytical model for repacking, 4 Discrete event simulation models. In our study, the considered input parameters λf, λh, ηf, ηh and μh are normalized by μf. For example, if the expected full-rate call holding time is then λf=2μf means that the expected full-rate inter call arrival time is 1min.
Conclusion
We proposed analytical and simulation models to investigate GSM channel assignment performance for half-rate and full-rate traffic. The channel assignment schemes under evaluation are random, best-fit, repacking and fair-repacking. Our study indicated that the repacking scheme can significantly improve the pnc performance over the other three schemes (about 20% improvements are observed). The probability pnc increases when the proportion of full-rate call traffic increases. We also observed
Acknowledgements
P.L.'s work was supported in part by National Science Council, Contract No. NSC88-2213-E009-079.
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(Video) GSM Channel Types by Dr. KAM
Copyright © 2000 Elsevier Science B.V. All rights reserved.
FAQs
What are the full rate and half rate channels in GSM? ›
Half-Rate Speech Channel (TCH/HS): the half-rate speech channel carries user speech which is digitalized and sampled at the rate half that of the full arte channel i.e.6.5 kbps, with GSM channel coding added to the digitalized speech, the full rate speech channel carries 11.4 kbps.
What is the difference between full rate traffic channel and half rate traffic channel? ›A full rate traffic channel (TCH/F) dedicates one slot per frame for a communication channel between a user and the cellular system. A half rate traffic channel (TCH/H) dedicates one slot per every two frames for a communication channel between a user and the cellular system.
What is full rate traffic channel in GSM? ›The Full Rate channel in GSM is identified as a 22.8Kbps gross bit rate channel. This channel is bidirectional enabling the transfer of speech or circuit switched data.
What are the traffic and control channels in GSM? ›In GSM networks, Control Channels are divided into three categories: Broadcast Channel (BCH), Common Control Channel (CCCH), and Dedicated Control Channel (DCCH).
What are GSM channels? ›GSM is a circuit-switched system that divides each 200 kHz channel into eight 25 kHz time-slots. GSM operates on the mobile communication bands 900 MHz and 1800 MHz in most parts of the world. In the US, GSM operates in the bands 850 MHz and 1900 MHz.
What are the frequency channels for GSM? ›GSM networks use multiple frequency bands, including 900 MHz, 1800 MHz, 850 MHz and 1900 MHz. The 900 MHz/1800 MHz combination is primarily used in Europe, Asia, Africa, the Middle East and Australia, whereas the 850 MHz/1900 MHz combination is used mainly in North and South America.
What is the most common traffic channel? ›- Organic Search: Traffic from the Search Engines.
- Referral: Traffic from other websites.
- Direct: Traffic from Typed in traffic, bookmarks or non browser sources.
- Paid Traffic: Traffic you have paid money to get to your website.
Traffic Channel or “TCH” means, a logical channel in a GSM or CDMA network which carries either encoded speech or user data; Sample 1Sample 2.
What is channel data rate? ›Data rate refers to the speed of data transfer through a channel. It is generally computed in bits per second (bps).
What are the two types of GSM channel? ›There are two main types of GSM channels viz. physical channel and logical channel. Physical channel is specified by specific time slot/carrier frequency.
What is GSM enhanced full rate? ›
EFR-GSM is the most widely used codec in the world. It operates at 12.2 kbps, the basic rate for GSM phones, and is in every GSM phone. It is also the highest-quality rate in the AMR codec.
What is GSM-900 channel? ›GSM-900 uses 890 - 915 MHz to send information from the Mobile Station to the Base Transceiver Station (BTS) (This is the “uplink”) and 935 - 960 MHz for the other direction (downlink), providing 124 RF channels spaced at 200 kHz. Duplex spacing of 45 MHz is used.
What is GSM control? ›GSM-Control SMS text message server is Microsoft Windows program used for 2-way remote control in automation and other applications using standard GSM/GPRS modems, cellular phones and GSM-network.
What is control channel in LTE? ›Control Channel can be either common channel or dedicated channel. A common channel means common to all users in a cell (Point to multipoint) while dedicated channels means channels can be used only by one user (Point to Point).
What are the 3 different types of GSM? ›The GSM network is divided into three major systems: the switching system (SS), the base station system (BSS), and the operation and support system (OSS).
What network is GSM LTE? ›GSM is the classic radio communication system in mobiles, whereas LTE is primarily the next generation of wireless technology for the system of cellular mobile communication. LTE and high-speed data transmission go hand in hand. LTE supports only data transmission, whereas GSM supports both data and voice.
What are the frequency bands for 5G GSM? ›The frequency bands for 5G networks come in two sets. Frequency range 1 is from 450 MHz to 6 GHz. Frequency range 2 is from 24.25 GHz to 52.6 GHz.
What is the frequency of GSM receiver? ›GSM900 is the original GSM system. It uses frequencies in the 900MHz band (numbered 1 to 124), and is designed for wide area cellular operation, with maximum output powers of 1W to 8W being allowed for mobile applications.
What are the frequency channels in LTE? ›| LTE Band Number | Frequency | Bandwidth (MHz) |
|---|---|---|
| LTE Band 34 | 2010 - 2025 MHz | 15 |
| LTE Band 35 | 1850 - 1910 MHz | 60 |
| LTE Band 36 | 1930 - 1990 MHz | 60 |
| LTE Band 37 | 1910 - 1930 MHz | 20 |
There are mainly two types of GSM logical channels: (i) Traffic channels (TCHs). (ii) Control channels (CCHs). Traffic channels carry digitally encoded user voice or user data and have identical formats of both forward link and reverse link.
What is the difference between traffic channel and control channel? ›
Traffic channels carry digitally encoded user voice or user data and have identical formats of both forward link and reverse link. Control channels carry signal and synchronization commands between the base station and mobile station. Other control channels are used only for forward and reverse link.
What are the two types of stream channels? ›Stream channels can be straight or curved, deep and slow, or rapid and choked with coarse sediments. The cycle of erosion has some influence on the nature of a stream, but there are several other factors that are important.