**5.2. Software setup**

13

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feedback

TCP/IP TCP/IP GPS PPS PPS NMEA NMEA

Fig. 3: Network structure of four-multi test-bed.

V. KTH FOUR-MULTI TEST-BED SETUP

and movable multi-antenna nodes. A software framework accompanies the hardware setup of the test-

*KTH four-multi* is a USRP-based wireless communication test-bed consisting of several stationary and movable multi-antenna nodes. A software framework accompanies the hardware setup of the test-bed which facilitates the rapid testing of multi-antenna schemes (see http://fourmulti.sourceforge.net/). In the following, the hardware and software structure

bed which facilitates the rapid testing of multi-antenna schemes (see http://fourmulti.sourceforge.net/).

The current version of the test-bed consists of six nodes where three of them are fixed and take the role of transmitting sources while the other three are movable receiving destinations. All the nodes are equipped with two vertically polarized dipole antennas spaced 20 cm apart which is 1.6 times of the carrier's wavelength. Twelve Ettus Research USRP N210 (see www.ettus.com) are used to govern the twelve antennas in the network. The source USRPs are equipped with the standard Ettus XCVR2450 RF dautherboards while the destination USRPs use custom boards to achieve sufficient noise figure and dynamic range. The output signal of each source USRP is amplified by a ZRL-2400LN power amplifier. Two Linux

The current version of the test-bed consists of six nodes where three of them are fixed and take the

role of transmitting sources while the other three are movable receiving destinations. All the nodes

are equipped with two vertically polarized dipole antennas spaced 20 cm apart which is 1.6 times

of the carrier's wavelength. Twelve Ettus Research USRP N210 (see www.ettus.com) are used to

govern the twelve antennas in the network. The source USRPs are equipped with the standard Ettus

XCVR2450 RF dautherboards while the destination USRPs use custom boards to achieve sufficient

noise figure and dynamic range. The output signal of each source USRP is amplified by a ZRL-

2400LN power amplifier. Two Linux computers control all the USRPs in the network. The network

The network is designed to work at 2.49 GHz center frequency with 12 MHz bandwidth. Syn-

chronization of the network is performed in three levels, namely time, frequency and transmit-receive

synchronizations. The time and transmit-receive synchronizations are done by means of a pulse-

per-second (PPS) signal (0-5 V, 1 Hz square wave) and a national marine electronics association

(NMEA) signal (an ASCII protocol that provides hour-minute-second time), respectively. Both signals

October 14, 2014 DRAFT

In the following, the hardware and software structure of the test-bed is described.

*KTH four-multi* is a USRP-based wireless communication test-bed consisting of several stationary

D3

CLK

CLK

computer

CLK

D2

D1

S3

S2

S1

CLK

backhaul

62 Contemporary Issues in Wireless Communications

computer

**Figure 3.** Network structure of four-multi test-bed.

**5. KTH four-multi test-bed setup**

of the test-bed is described.

**5.1. Hardware setup**

structure of four-multi test-bed is illustrated in Fig. 3.

*A. Hardware Setup*

master node

The four-multi software framework has been developed in C++(see http://fourmulti.source‐ forge. net/). It runs on two Linux computers separately. One of the computers controls the three source nodes while the other one controls the three destination nodes connected to them via Ethernet connections. The sources' computer generates the transmitted frames and feeds them to the source nodes while the destinations' computer process the received frames at the destination nodes. A TCP/IP connection between the source and the destination computers provides the feedback links. Backhaul communication among the source nodes is also implemented by the help of TCP/IP connections between the source computer and the source nodes.

The framework contains a toolbox for coding and modulation (AMC and OFDM1) which was used in the implementations of the next two sections. The KTH four-multi Modula‐ tion and coding toolbox includes an LDPC channel encoder/decoder, a QAM modulator/ demodulator and an OFDM modulator/demodulator. The specification of these built-in functions is summarized in Table 1.


**Table 1.** Modulation and coding toolbox specifications.
