Added checking for Volk presence according to @dholm #4 pull request.
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 572f87b..39e078b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -89,6 +89,7 @@
 # Find gnuradio build dependencies
 ########################################################################
 find_package(GnuradioRuntime)
+find_package(Volk)
 find_package(CppUnit)
 find_package(Doxygen)
 
@@ -103,6 +104,9 @@
 if(NOT GNURADIO_RUNTIME_FOUND)
     message(FATAL_ERROR "GnuRadio Runtime required to compile gsm")
 endif()
+if(NOT VOLK_FOUND)
+    message(FATAL_ERROR "Volk library required to compile gsm")
+endif()
 if(NOT CPPUNIT_FOUND)
     message(FATAL_ERROR "CppUnit required to compile gsm")
 endif()
diff --git a/cmake/Modules/FindVolk.cmake b/cmake/Modules/FindVolk.cmake
new file mode 100644
index 0000000..425eb01
--- /dev/null
+++ b/cmake/Modules/FindVolk.cmake
@@ -0,0 +1,26 @@
+INCLUDE(FindPkgConfig)
+PKG_CHECK_MODULES(PC_VOLK volk)
+
+FIND_PATH(
+    VOLK_INCLUDE_DIRS
+    NAMES volk/volk.h
+    HINTS $ENV{VOLK_DIR}/include
+        ${PC_VOLK_INCLUDEDIR}
+    PATHS /usr/local/include
+          /usr/include
+)
+
+FIND_LIBRARY(
+    VOLK_LIBRARIES
+    NAMES volk
+    HINTS $ENV{VOLK_DIR}/lib
+        ${PC_VOLK_LIBDIR}
+    PATHS /usr/local/lib
+          /usr/local/lib64
+          /usr/lib
+          /usr/lib64
+)
+
+INCLUDE(FindPackageHandleStandardArgs)
+FIND_PACKAGE_HANDLE_STANDARD_ARGS(VOLK DEFAULT_MSG VOLK_LIBRARIES VOLK_INCLUDE_DIRS)
+MARK_AS_ADVANCED(VOLK_LIBRARIES VOLK_INCLUDE_DIRS)
diff --git a/lib/CMakeLists.txt b/lib/CMakeLists.txt
index f420820..228897a 100644
--- a/lib/CMakeLists.txt
+++ b/lib/CMakeLists.txt
@@ -42,7 +42,7 @@
 )
 
 add_library(gnuradio-gsm SHARED ${gsm_sources})
-target_link_libraries(gnuradio-gsm ${Boost_LIBRARIES} ${GNURADIO_RUNTIME_LIBRARIES}  
+target_link_libraries(gnuradio-gsm ${Boost_LIBRARIES} ${GNURADIO_RUNTIME_LIBRARIES} ${VOLK_LIBRARIES}
     boost_iostreams
     boost_system
     boost_filesystem