This document discusses cell coverage and ranges for LTE networks. Key points include: - LTE aims to support cell radii up to 5 km while still enabling coverage of 100km or more, to support high-speed rail and wide-area deployments. - Cell sizes in LTE can range from a few meters across in indoor environments to radii of 100km or more for large rural cells. - The random access preamble formats and timing advance mechanisms in LTE are designed to support the maximum cell size of 100km radius to accommodate the largest expected propagation delays. - A guard period duration of 700 μs supports one-way propagation delays of around 100km, allowing LTE to potentially support cell

1. Long Range Cell Coverage for LTE
Yi-Hsueh Tsai
lucas@iii.org.tw
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2. 1.2.1.4 Mobility and Cell Ranges
• LTE is required to support communication with terminals
moving at speeds of up to 350 km/h, or even up to 500 km/h
depending on the frequency band. The primary scenario for
operation at such high speeds is usage on high-speed
trains – a scenario which is increasing in importance across
the world as the number of high-speed rail lines increases
and train operators aim to offer an attractive working
environment to their passengers. These requirements mean
that handover between cells has to be possible without
interruption – in other words, with imperceptible delay and
packet loss for voice calls, and with reliable transmission
for data services.
• These targets are to be achieved by the LTE system in
typical cells of radius up to 5 km, while operation should
continue to be possible for cell ranges of 100km and more,
to enable wide-area deployments.

3. 5.4.1 Physical Layer Parameters for LTE
• LTE aims at supporting a wide range of cellular deployment
scenarios, including indoor, urban, suburban and rural
situations covering both low and high UE mobility
conditions (up to 350 or even 500 km/h). The cell sizes may
range from home networks only a few meters across to large
cells with radii of 100 kilometers or more.
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4. 17.3.1.3 Step3: Layer2/Layer3 Message
• If the UE successfully receives the RAR, the UE minimum
processing delay before message 3 transmission is 5ms minus
the round-trip propagation time. This is shown in Figure 17.3
for the case of the largest supported cell size of 100km.
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Figure17.3: Timing of the message 3 transmission

5. 17.4.2.2 PRACH Formats
• Four Random Access preamble formats are defined for
Frequency Division Duplex (FDD) operation. Each format is
defined by the durations of the sequence and its CP, as listed
in Table17.1. The format configured in a cell is broadcast in
the System Information.
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Table17.1: Random access preamble formats.

6. 17.4.2.3 Sequence Duration
• Maximum round-trip time. The lower bound for
TSEQ must allow for unambiguous round-trip time
estimation for a UE located at the edge of the largest
expected cell (i.e. 100 km radius), including the
maximum delay spread expected in such large cells,
namely 16.67 µs. Hence
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7. 17.4.2.4 CP and GT Duration
• For formats 1 and 3, the CP is dimensioned to address the
maximum cell range in LTE, 100 km, with a maximum
delay spread of d≈16.67 µs. In practice, format 1 is
expected to be used with a 3-subframe PRACH slot; the
available GT in 2 subframes can only address a 77 km cell
range. It was chosen to use the same CP length for both
format 1 and format 3 for implementations implicitly. Of
course, handling larger cell sizes than 100 km with
suboptimal CP dimensioning is still possible and is left to
implementation.
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8. 18.2.2.1 Initial Timing Advance
• After a UE has first synchronized its receiver to the
downlink transmissions received from the eNodeB (see
Section 7.2), the initial timing advance is set by means of
the random access procedure described in Section 17.3. This
involves the UE transmitting a random access preamble
from which the eNodeB estimates the uplink timing and
responds with an 11-bit initial timing advance command
contained within the Random Access Response (RAR)
message. This allows the timing advance to be configured
by the eNodeB with a granularity of 0.52 µs from 0 up to a
maximum of 0.67 ms,1 corresponding to a cell radius of
100km.
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9. 18.2.2.1 Initial Timing Advance
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Figure 10.13: Timing diagram of the downlink HARQ (SAW) protocol
Figure10.14: Timing diagram of the uplink HARQ (SAW) protocol

10. 18.2.2.1 Initial Timing Advance
• The timing advance was limited to this range in order to
avoid further restricting the processing time available at the
UE between receiving the downlink signal and having to
make a corresponding uplink transmission (see Figures
10.13 and 10.14). In any case, a cell range of 100 km is
sufficient for most practical scenarios, and is far beyond
what could be achieved with the early versions of GSM, in
which the range of the timing advance restricted the cell
range to about 35 km. Support of cell sizes even larger than
100 km in LTE is left to the eNodeB implementation to
handle.
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11. 23.4.1 Accommodation of Transmit–
Receive Switching
• The LTE specifications support a set of guard period durations
ranging (non- contiguously) from 1 to 10 OFDM symbols for
the normal CP (or from 1 to 8 OFDM symbols for the
extended CP). A duration of 1 OFDM symbol should be
sufficient for many of the anticipated cellular deployments of
LTE (up to around 2 km nominal cell radius for γ =2), whereas
at the other end of the scale, guard period durations of the
order of 700 µs support one-way propagation-path delays of
the order of 100km.
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12. References
1) LTE The UMTS Long Term Evolution from Theory
to Practice Ed2
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