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...s. Therefore define h (k) m,q = h (k) q e2πjφkm ,k = 1,2. For clarity we omit the subindices m,q in the following derivation. The max-log MAP bit metric for bit b of the desired stream x1 is given as =-=[28]-=- λ i 1 (y,b)≈ min x1∈χ i 1,b ,x2∈χ2 = min x1∈χ i 1,b ,x2∈χ2 ‖y−h1x1− h2x2‖ 2 { ‖y‖ 2 +‖h1x1‖ 2 − (2y1x ∗ 1) R +(2p12x ∗ 1x2) R − (2y2x ∗ 2) R + ‖h2x2‖ 2} where y1 = h H 1 y be the matched filter outpu...

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...ture wireless systems [25, 26]. However, it is well where h (1) q and h (2) q known that MMSE detection for non Gaussian alphabets in low dimensional systems (low number of interferers) is suboptimal =-=[27]-=- and moreover MMSE detection cannot exploit the interference structure. The frequency domain MMSE filter Mq is given as Mq = ( σ 2 P −1 + H H )−1 H q Hq Hq where P is the diagonal power distribution m...

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...tely afterwards (refractory period). Therefore data transmission can only take place in the refractory period. However, this period must not be very long because otherwise the system becomes unstable =-=[32]-=-. In OpenAirMesh we follow a similar approach as in [3] for distributed timing synchronization. It is based on the two physical channels CHSCH and MRSCH (see Table V) which are transmitted in alternat...

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...nd are not able to operate indoors. Therefore we will take a distributed network synchronization approach.9 In nature, distributed synchronization scheme can be observed on the flashing of fireflies =-=[29]-=-. Recently, this natureinspired scheme has been applied to synchronization in wireless networks [30–33]. However, most of these works consider the isolated synchronization problem and neglect the actu...

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...link-level algorithms without using the radio interface [1]. The OpenAirInterface can also be used to perform channel measurements which can be used for channel characterization and capacity analysis =-=[2]-=-. Apart from a general overview of OpenAirInterface, in this paper we present OpenAirMesh—a specification of wireless2 mesh network and its implementation on the OpenAirInterface platform. OpenAirMes...

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...Hydra testbed of the University of Texas in Austin [9] is based on the GNU radio platform while the WAPRnet testbed [10] is based on WARP platform. The WiTestLab from the Polytechnic Institute of NYU =-=[11]-=- has been experimenting with both platforms. Another testbed example it the Cognitive Radio Testbed from Berkley [12], which uses the Berkeley Emulation Engine 2 (BEE2) [13] as an implementation platf...

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...10] is based on WARP platform. The WiTestLab from the Polytechnic Institute of NYU [11] has been experimenting with both platforms. Another testbed example it the Cognitive Radio Testbed from Berkley =-=[12]-=-, which uses the Berkeley Emulation Engine 2 (BEE2) [13] as an implementation platform. Compared to the OpenAirInterface platform, the GNU radio project does not provide a full reference design, but o...

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...ess open-access research platform (WARP) from Rice University [8]. For example, the Hydra testbed of the University of Texas in Austin [9] is based on the GNU radio platform while the WAPRnet testbed =-=[10]-=- is based on WARP platform. The WiTestLab from the Polytechnic Institute of NYU [11] has been experimenting with both platforms. Another testbed example it the Cognitive Radio Testbed from Berkley [12...

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...I-A) and is thus restricted to two antennas. Therefore we can process up to two spatial streams coming from two different CHs. The extension of the receiver structure to more antennas can be found in =-=[21]-=-. A. Dual-stream MIMO Receiver Architecture In this section, after the general overview of the receiver structure in Subsection IV-A1, we describe two different dualstream multi-antenna demodulators, ...

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...cus on a particular layer, such as the physical layer, the link layer or the network layer. A good overview of testbeds that focus on the physical layer and especially MIMO communications is given in =-=[4, 5]-=-. Most of the testbeds that provide both physical and link layer functionalities (like OpenAirInterface) are either based on the Universal Software Radio Peripheral (USRP) from Ettus Research [6] toge...

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...ge and channel bandwidth than CBMIMO1. The tuning range per III. OPENAIRMESH SPECIFICATION In this section we present the specification of OpenAirMesh, a mesh network built using the OpenAirInterface =-=[18]-=-. We start off by describing the network topology in Subsection III-A. In Subsection III-B we describe the layer 2 and finally in Subsection III-C the physical layer. A more detailed specification can...

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...cus on a particular layer, such as the physical layer, the link layer or the network layer. A good overview of testbeds that focus on the physical layer and especially MIMO communications is given in =-=[4, 5]-=-. Most of the testbeds that provide both physical and link layer functionalities (like OpenAirInterface) are either based on the Universal Software Radio Peripheral (USRP) from Ettus Research [6] toge...

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...ications. However, no software modem exists for this platform. Last but not least we mention here the two testbeds developed within the EASY-C project 1 that were set up in Berlin [14] and in Dresden =-=[15]-=- (both Germany). The project is a cooperation between German universities, research centers and industry and focuses on LTE-Advanced technologies. However, both testbeds use proprietary hardware and s...

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...e spectral efficiency of the data streams. Different wideband scheduling policies taking into account both queuing measures from RLC and channel quality feedback can be accommodated (see for instance =-=[20]-=-). Channel quality information is signaled between corresponding MAC-layers based quantized wideband channel estimates received from PHY. C. Physical Layer The physical layer of the platform uses orth...

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...l diversity, while the performance of the MMSE receiver hardly improves. This is due to the fact that the max-log MAP receiver has full diversity gain while MMSE receiver loses one order of diversity =-=[34]-=-. In a LOS Ricean fading channel, the performance of the max-log MAP receiver is better than in a Rayleigh fading11 10 0 10 0 10 −1 FER Stream 1 10 −1 FER Stream 1 10 −2 MMSE, SNR=5dB MMSE, SNR=10dB ...

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...n. In the emulation mode, the physical layer is abstracted and emulated over the ethernet. This approach allows to test and investigate MAC and link-level algorithms without using the radio interface =-=[1]-=-. The OpenAirInterface can also be used to perform channel measurements which can be used for channel characterization and capacity analysis [2]. Apart from a general overview of OpenAirInterface, in ...

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...een base-stations both on the media access (MAC) and the physical (PHY) layer. The distributed synchronization algorithm proposed in this paper can be interpreted as a form of firefly synchronization =-=[3]-=-. Related Work: Many people have recognized the advantages of testbeds for wireless networks. However, many of them focus on a particular layer, such as the physical layer, the link layer or the netwo...

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...ther based on the Universal Software Radio Peripheral (USRP) from Ettus Research [6] together with the GNU software radio [7] or the wireless open-access research platform (WARP) from Rice University =-=[8]-=-. For example, the Hydra testbed of the University of Texas in Austin [9] is based on the GNU radio platform while the WAPRnet testbed [10] is based on WARP platform. The WiTestLab from the Polytechni...

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...esearch [6] together with the GNU software radio [7] or the wireless open-access research platform (WARP) from Rice University [8]. For example, the Hydra testbed of the University of Texas in Austin =-=[9]-=- is based on the GNU radio platform while the WAPRnet testbed [10] is based on WARP platform. The WiTestLab from the Polytechnic Institute of NYU [11] has been experimenting with both platforms. Anoth...

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...f by describing the network topology in Subsection III-A. In Subsection III-B we describe the layer 2 and finally in Subsection III-C the physical layer. A more detailed specification can be found in =-=[19]-=-. A. Network Topology In OpenAirMesh, the network is organized in clusters, where nodes can either take the role of a cluster-heads (CHs) or a mesh router (MR). CHs are typically the best-connected no...

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...h amongst the finite available points, the point closest to the calculated continuous value is selected. The reduced complexity max-log MAP detector has a much lower complexity than the MMSE receiver =-=[22]-=-. Furthermore, it can be implemented without any division and therefore it is numerically more stable than the MMSE receiver. B. Network Synchronization The dual-stream MIMO receiver described above r...

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...e nulling out the interference in the latter case. Linear MMSE filters exhibit better performance compared to ZF ones and are thus being considered as favorable candidates for future wireless systems =-=[25, 26]-=-. However, it is well where h (1) q and h (2) q known that MMSE detection for non Gaussian alphabets in low dimensional systems (low number of interferers) is suboptimal [27] and moreover MMSE detecti...

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...n [4, 5]. Most of the testbeds that provide both physical and link layer functionalities (like OpenAirInterface) are either based on the Universal Software Radio Peripheral (USRP) from Ettus Research =-=[6]-=- together with the GNU software radio [7] or the wireless open-access research platform (WARP) from Rice University [8]. For example, the Hydra testbed of the University of Texas in Austin [9] is base...

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...de both physical and link layer functionalities (like OpenAirInterface) are either based on the Universal Software Radio Peripheral (USRP) from Ettus Research [6] together with the GNU software radio =-=[7]-=- or the wireless open-access research platform (WARP) from Rice University [8]. For example, the Hydra testbed of the University of Texas in Austin [9] is based on the GNU radio platform while the WAP...

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...ificantly more processing power and bandwidth than CBMIMO1 and will be used for future applications. It comprises two FPGAs: one Xilinx XC5VLX330 for real-time embedded signal processing applications =-=[17]-=- and one Xilinx XC5VLX110T for control. The card uses an eight-way PCI express interface to communicate with the host PC. The card employs four high-speed A/D and D/A converters from Analog Devices (A...

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...e nulling out the interference in the latter case. Linear MMSE filters exhibit better performance compared to ZF ones and are thus being considered as favorable candidates for future wireless systems =-=[25, 26]-=-. However, it is well where h (1) q and h (2) q known that MMSE detection for non Gaussian alphabets in low dimensional systems (low number of interferers) is suboptimal [27] and moreover MMSE detecti...