1.
General
1. 1. Scope
The scope of this document is to detail the WALKair system specification as per
Version 3 of the WALKair system.
1. 2. WALKairTM SYSTEM AND BUILDING BLOCKS
The WALKair PMP system consists of a Base Station (BS) with multiple Terminal
Stations (TS). The BS is connected by radio channels to all TS.
The Base Station is a modular hub, connected to the Telecom switches on one side
and to the service areas, via the Terminal Stations, on the other side. Each Terminal
Station provides various Telecom services.
The following diagram illustrates the system architecture.
SNMP based NMS
Standard platform Base Station (BS) Terminal Stations (TS)
Sector
NMS RFU +
Antenna Antenna
PABX
Workst at ion
ISDN
. PRI
RFU
.
Frame
To:
. BU Relay
Telecom backbone
ISP RFU +
IF MUX Antenna
ISDN
BRI
Voice & BU
Data Ethernet Wo rk s ta tio n
Figure 1: WALKair’s System Architecture
1. 1.1. Base Station (BS)
The Base Station consists of several sectors. Each sector contains one or more
(up to 8 in the 3.5GHz band and up to 16 in the 10.5GHz and 26GHz bands)
Basic Units (BU), an IF MUX, RFU and an antenna.
1. 2.1.1. Basic Unit (BU)
The main building blocks of the BU are: the modem, the telecom interface
cards and the IF module. Each BU converts the modulated IF signal to
telecom voice/data towards the telecom port, and vice versa.
The modem is implemented on the motherboard, which is identical on all
BUs. The interface cards and the IF module are implemented on
daughterboards, and therefore allow maximum flexibility.
Each BU contains up to three interfaces to the telecom switches or other
network equipment. Each BU transmits and receives one carrier and, by
employing TDMA mechanism, handles the traffic of several remote
Terminal Stations (typically 2-10, maximum 16). Malfunctioning of a single
BU does not affect the others.
1. 2.1.2. IF MUX
The IF MUX combines the IF signals from/to the various BUs into a single
coax cable that goes up to the roof top, where the RFU and antenna
subsystems are located. Up to 8 or 16 BUs (depending on the IF-MUX
type) may operate together combined by the same IF-MUX.
1. 2.1.3. RFU
The RFU is an RF transceiver. In the transmit direction, the RFU converts
the IF to RF, amplifies the signal to its right level and transmits it through
the antenna. In the receive direction, the RFU receives the RF signal from
the antenna, and converts it to IF. It is mounted near the antenna. The
system has more than one type of an RFU, each serving a different radio
frequency band. 3.5Ghz , 10.5Ghz and 26Ghz. All RFUs are isolated from
the indoor equipment, and operate with BUs and IF-MUX.
1. 2.1.4. Antenna
The antenna is a sector type. It covers an angular area. Several sector
antennas (4, 6 or 8), each with its own RFU, may cover a whole service
area (cell).
1. 2.1.5. BS Powering
The BS is powered by a standard Telecomm DC source (48V) to the
indoor unit.
1. 1.2. Terminal Station (TS)
A Terminal Station consists of a single BU (different from BS) and an integrated
RFU and antenna subsystem.
1. 2.1.6. BU
The BU operation is similar to the one at the Base Station. A single coax cable
carries IF signal, that connects it to the RFU which is installed at the roof top.
1. 2.1.7. RFU and Antenna
The RFU is an RF transceiver. In the transmit direction it converts IF to RF, and in
the receive direction, it converts RF to IF. The antenna is an integral part of the
RFU in the 3.5GHz and 10.5GHz bands, and attached to the RFU in the 26GHz
band. The antenna is a directional antenna, that is directed towards the BS
location.
1. 2.1.8. TS Powering
The TS is powered either by an AC (110/220V) source or a DC (48V) source to
the indoor unit.
2. System Performance
2. 1. Radio access method
Multi Carrier/TDMA /FDD
Multi carrier is used among several modular units in the base station
TDMA is used among several Terminal Stations that are communicating with a
basic modular unit of the base station. Transmission of terminal stations (uplink) is
TDMA. Transmission of base station (downlink) is TDM.
FDD - Different frequencies are used for upstream and downstream
2. 2. Modulation Type
64QAM with convolutional coding at rate 2/3.
Coherent Demodulation.
2. 3. Frequency bands supported
3.4-3.6GHz, 10.15-10.65GHz, 24.5-26.5GHz
2. 4. Supported distance with BER=10-9.
3.5Ghz: 300m - 10Km at near line of sight.
10.5Ghz: 300m - 10Km at line of sight.
26GHz: 300m - 4 km at line of sight
2. 5. Number of terminal stations per one Carrier
up to 16.
2. 6. Number of Carriers per one Sector
3.5Ghz: 8.
10.5Ghz: 16
26GHz: 16
2. 7. Bandwidth per single user
64Kbps to 4.096Mbps. Granularity of 64Kbps.
2. 8. Transmission bit rate in the air
Maximum of net payload traffic - 4.096Mbps. Gross bit rate is 4.480Mbps. Symbol rate
is 1.12Msymbol/Sec.
2. 9. BER vs. Pin
The following table is the spec for BER in RF back 2back setup, as a function of
power at input to RFU. Spec applies to both downstream and upstream.
3.5 GHz and 10.5 GHz:
Power at input to RFU Maximum allowed
BER
-87 dBm 10-9
-89 dBm 10-6
-90 dBm 10-3
26.5 GHz:
Power at input to RFU Maximum allowed
BER
-85 dBm 10-9
-87 dBm 10-6
-88 dBm 10-3
2. 10. Required C/I
For BER: Required C/I is:
10-9 21 dB
10-6 19 dB
10-3 18 dB
2. 11. Channel Interference
1. 1.3. CCI
Co-channel interference is better than EN 301 021 5.4.4: The receiver can
tolerate co-channel interference (interfering signal in the same channel) of xx
below the wanted signal (see table)
Spec of performance with wanted signal at operating point of -83 dBm (power at
input to BS RFU):
DOWNSTREAM CCI UPSTREAM CCI C/I
C/I
Required CCI to 21 dB 21 dB
assure BER better
than 10^(-6)
Required CCI to 23 dB 23 dB
assure BER better
than 10^(-9)
1. 1.4. ACI (N+1)
The receiver can tolerate Adjacent Channel Interference of xx above the wanted
signal (see table). Spec of performance with wanted signal at operating point of -
83 dBm (power at input to BS RFU):
DOWNSTREAM UPSTREAM
Power of ACI relative Power of ACI relative
to signal to signal
Maximum ACI to 18 dB 23 dB
assure BER better
than 10^(-6)
Maximum ACI to 15 dB 15 dB
assure BER better
than 10^(-9)
At 1.75MHz channel spacing, the receive filters attenuate Adjacent Channel
Interference (ACI) by at least 38dB, relative to the wanted signal
1. 1.5. ACI (N+2)
The receiver can tolerate N+2 Adjacent Channel Interference of xx above the
wanted signal (see table).
Spec of performance with wanted signal at operating point of -83 dBm (power at
input to BS RFU):
DOWNSTREAM UPSTREAM
Power of ACI relative Power of ACI relative
to signal to signal
Maximum ACI to 30 dB 30 dB
assure BER better
than 10^(-6)
Maximum ACI to 30 dB 30 dB
assure BER better
than 10^(-9)
2. 12. CW interference
For a receiver operating at the RSL of -83dBm, the introduction of a CW interferer at a
level of + 30 dB with respect to the wanted signal and at any frequency up to five
times the carrier center frequency, excluding frequencies on either side of the center
frequency of the wanted RF channel by up to 8.75MHz (i.e. 500 % of the co-polar
channel spacing), does not cause BER worse than 10-6.
2. 13. Flat Fading Tracking
BER of 10-9 is supported when tested under the following conditions:
Triangular fading pattern (over time),
Fading peak to peak magnitude of 10dB,
Link attenuation is such that at the input to the TS RFU, the received power varies
anywhere between -80dBm to -60dBm,
Maximum instantaneous fading speed is 70 dB/Sec.
2. 14. 99% Occupied Bandwidth
BS and TS (typical): 1.5MHz.
2. 15. Multipath performance (Modem Signature)
Multipath is handled by an adaptive equalizer, which learns the channel’s
characteristics during initialization phase, and tracks the changes. It can handle
multiplath and allows for Near LOS in 3.5GHz
Modem signature with two path model, with delay of 84 nsec (between the two paths),
for BER of 10^(-9):
1. Signature is symmetric for minimum phase and nonminimum phase multipath.
2. Signature has a depth of 26 dB.
3. Signature has a width of +-600 kHz (in downstream direction), and width of +-400
kHz (in upstream direction).
1. 1.6. DS Signature plot for error free performance
1. 1.7. US Signature plot for error free performance
