Gsm Data Rate Calculation

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GSM Data Rate Calculator (HSCSD/Theoretical)

Calculate the theoretical maximum data throughput for a GSM connection based on allocated timeslots and coding scheme.

Gross Air Interface (Raw ~33.85 kbps/TS) Standard CSD (Net 9.6 kbps/TS) Enhanced CSD (Net 14.4 kbps/TS)
Typically 1-4 for HSCSD, up to 8 theoretical.

Calculated Data Rate:

0 kbps

function calculateGSMRate() { var ratePerTS = parseFloat(document.getElementById("codingScheme").value); var numTimeslots = parseInt(document.getElementById("numTimeslots").value); var resultDiv = document.getElementById("gsmResult"); var rateOutputSpan = document.getElementById("rateOutput"); if (isNaN(numTimeslots) || numTimeslots 8) { alert("Please enter a valid number of timeslots between 1 and 8."); return; } var totalRateKbps = ratePerTS * numTimeslots; // Format output to maximum 3 decimal places for gross rate, 1 for CSD var formattedRate; if (ratePerTS > 30) { formattedRate = totalRateKbps.toFixed(3); } else { formattedRate = totalRateKbps.toFixed(1); } rateOutputSpan.innerHTML = formattedRate; resultDiv.style.display = "block"; }

Understanding GSM Data Rates and Timeslots

The Global System for Mobile Communications (GSM) is a second-generation (2G) digital cellular network standard. While primarily designed for voice, GSM supports data transmission through various methods. Understanding GSM data rates requires looking at its underlying Time Division Multiple Access (TDMA) frame structure.

The GSM Frame and Gross Rate

A GSM frequency carrier transmits at a gross bit rate of approximately 270.833 kbps. This carrier is divided in time into TDMA frames, each lasting approximately 4.615 milliseconds. Every frame is further divided into 8 time slots (TS0 to TS7).

Therefore, the gross air interface rate available per single timeslot is the total rate divided by eight:
270.833 kbps / 8 ≈ 33.854 kbps per timeslot.

This "gross" rate includes necessary overhead for synchronization, guard times, and error correction, meaning the actual usable data rate for the user is significantly lower.

Circuit Switched Data (CSD) and HSCSD

Before packet-switched technologies like GPRS and EDGE became prevalent, GSM used Circuit Switched Data (CSD). CSD allocates dedicated timeslots for data, similar to a voice call.

  • Standard CSD: Due to heavy Forward Error Correction (FEC) coding required to ensure reliable transmission over the radio interface, a single timeslot typically provides a net user data rate of just 9.6 kbps.
  • High-Speed CSD (HSCSD): To achieve higher speeds, HSCSD allows a single user to utilize multiple timeslots simultaneously within a TDMA frame. For example, using 4 timeslots at the standard CSD rate would yield 4 x 9.6 kbps = 38.4 kbps. Later enhancements allowed for reduced coding, pushing the per-timeslot rate up to 14.4 kbps in good radio conditions.

This calculator allows you to estimate theoretical rates by selecting either the gross air rate or standard net CSD rates and multiplying them by the number of allocated timeslots.

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